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AGRONOMY 

A  COURSE  IN  PRACTICAL  GARDENING 
FOR  HIGH  SCHOOLS 


BY 

WILLARD  NELSON  CLUTE 

AUTHOR  OF  "laboratory  BOTANY  FOR  HIGH  SCHOOLS,"  "FLORA  OF  THE 

UPPER  SUSQUEHANNA,"  "OUR  FERNS  IN  THEIR  HAUNTS," 

"fern  ALLIES  OF  NORTH  AMERICA,"  ETC. 


GINN  AND  COMPANY 

BOSTON  •  NEW  YORK  •  CHICAGO  •  LONDON 


COPYRIGHT,  1913,  BY  WILLARD  KELSON  CLUTE 
ALL    RIGHTS    RESERVED 

913.1 


GINN  ANU  COMPANY  •  PRO- 
PRIETORS •  BOSTON  •  U.S.A. 


PREFACE 

This  book  has  been  prepared  to  meet  the  needs  of  high 
schools  in  cities  and  towns  where  agriculture  is  taught,  and 
in  which  the  problems  that  confront  the  teacher  are  in  some 
respects  different  from  those  that  come  up  in  rural  communi- 
ties. The  envu-onment  of  the  city  child  makes  it  undesirable 
to  emphasize  in  his  case  the  growing  of  stock,  the  production 
and  care  of  milk,  the  breeding  of  animals,  and  the  cultivation 
of  field  crops.  There  is,  however,  much  information  of  a 
practical  nature  regarding  the  cultivation  of  plants  which  he 
finds  necessary  for  the  fullest  enjoyment  of  his  surroundings. 
Though  not  engaged  in  growing  crops  for  a  livelihood,  he  is, 
nevertheless,  interested  in  the  cultivation  of  vegetables  and 
flowers,  the  making  of  lawns  and  their  care,  the  planting  of 
shrubbery,  the  trimming  of  trees,  and  similar  matters.  In  the 
present  volume  it  has  been  the  aim,  therefore,  to  develop  the 
subject  of  agriculture  from  the  urban  viewpoint,  though 
.  *  the  matters  discussed  are  fundamental  to  any  system  of  cul- 
S^  tivatuig  plants  and  are  as  applicable  to  rural  communities  as 
elsewhere.  Furthermore,  it  is  expected  that  the  book  will 
^  also  serve  as  a,  practical  guide  to  that  part  of  the  general 
S^  public  which,  though  no  longer  in  school,  takes  an  interest 

^  101  the  fcultivation  of  plants  in  lawn,  garden,  and  orchard. 
>i\       Agronomy,  as  outlined  in  the  following  pages,  is  regarded 
^^fi^as  a  division  of  agriculture  coordinate  with  animal  husbandry. 
^  The  latter  division,  though  often  included  in  books  of  this 
kind,  is  as  distinct  from  agronomy  as  zoology  is  from  botany, 
and  has  been  omitted  from  this  book  partly  because  the  sub- 
ject of  agronomy  is  alone  sufficient  for  one  semester's  work, 


442842 


vi  AGRONOMY 

and  partly  because  city  children  are  not  brought  much  into 
contact  with  farm  animals.  Animal  husbandry  may  well  be 
tauglit  as  a  separate  course,  and,  if  given  in  the  semester  fol- 
lowing that  m  which  agronomy  is  given,  will  afford  the  pupil 
a  year's  continuous  work  in  agriculture.  The  practical  nature 
of  the  matter  here  presented  has  been  proved  by  several  sea- 
sons' work  with  classes  in  a  large  city  high  school.  No  direc- 
tions for  work  have  been  given  that  have  not  been  tried  out 
with  such  classes. 

Agronomy  differs  from  the  usual  botanical  course  of  the 
high  school  in  that  it  is  largely  the  practice  of  an  art  rather 
than  the  study  of  a  science.  It  seeks  to  make  the  student 
physically  proficient  as  well  as  mentally  alert.  Although 
usually  given  after  a  course  in  botany,  it  is  by  nature  an 
excellent  introduction  to  the  more  technical  study,  since  it 
enables  the  student  to  bring  to  bear  upon  it  a  considerable 
first-hand  knowledge  of  plants  and  plant  habits.  In  the  high- 
school  curriculum  botany  may  be  considered  as  existing  for 
the  sake  of  the  drill  it  gives  in  observation  and  deduction, 
as  well  as  for  the  information  it  affords,  and  it  is  therefore 
proper  that  it  should  be  based  largely  upon  experiment.  In 
agronomy,  however,  experiment  has  a  much  smaller  place. 
The  fundamentals  have  so  long  been  a  matter  of  common 
knowledge  that  they  need  not  be  made  the  subjects  for  ex- 
periment, though  the  possibility  of  proving  any  phase  of  the 
work  by  this  means  should  not  be  overlooked. 

The  course  in  agronomy  here  presented  is  designed  to 
cover  a  half  year  of  work  in  the  laboratory  and  school  garden 
and  to  be  given  in  the  spring  semester.  It  is  essentially  an 
outdoor  course  in  doing  things,  with  the  culture,  propagation, 
and  amelioration  of  plants  as  the  central  theme.  It  presup- 
poses a  school  garden  in  which  the  pupil  can  carry  out  the 
work  of  cultivating  and  framing  plants,  and  the  chief  end  of 
the  course  will  be  missed  if  this  book  is  used  merely  as  a 


PREFACE  vii 

convenient  source  of  material  for  recitations.  Few  schools  are 
so  situated  as  to  make  the  possession  of  a  school  garden  abso- 
lutely impossible.  If  the  school  grounds  are  not  large  enough, 
a  vacant  lot  in  the  vicinity  may  be  secured  by  rent  or  pur- 
chase, or  the  home  garden  of  one  of  the  pupils  may  be  used. 
Some  successfully  managed  school  gardens  are  ten  minutes' 
walk  from  the  school  building.  Wherever  located  the  garden 
ought  to  be  securely  fenced  against  the  depredations  of  the 
small  boy  and  other  irresponsible  folk,  and  a  certain  degree 
of  permanency  should  be  secured  for  the  plantings,  if  possi- 
ble, since  at  least  part  of  the  plants  grown  will  be  perennials, 
which  improve  with  the  years  if  left  undisturbed.  Whenever 
practicable,  the  school  garden  should  be  a  part  of  the  school 
property. 

Classes  seldom  need  to  be  encouraged  to  take  an  mterest 
in  gardening,  but  the  teacher  should  see  to  it  that  the  work 
is  properly  planned  in  advance,  that  time  is  allowed  for  culti- 
vating the  crops,  and  that  such  experiments  are  carried  on  in 
the  experimental  plots  as  will  deepen  the  interest  and  value 
of  the  work  to  the  student.  The  food,  fiber,  and  drug  plants 
little  known  in  the  region  may  be  grown,  the  many  varieties 
of  common  vegetables  may  be  tested,  and  attractive  flowers 
cultivated.  Room  should  also  be  found  for  growing  all  sorts 
of  aberrant  plants  that  may  be  discovered  by  the  class,  such 
as  those  possessing  double  flowers,  fasciated  stems,  color  varia- 
tions, and  variations  in  the  cutting  of  leaves.  As  a  general 
thing,  the  crops  planted  should  be  such  as  mature  before 
school  closes  for  the  summer  or  which  do  not  mature  until 
autumn.  In  the  first  group  are  lettuce,  spinach,  cress,  radishes, 
onions,  and  turnips ;  in  the  second  are  carrots,  parsnips,  and 
salsify.  The  many  forms  of  radishes  now  offered  by  seeds- 
men are  excellent  subjects  for  showing  the  great  variation 
that  may  occur  in  a  single  plant  part.  A  few  experiments 
may  be  carried  on  for  a  series  of  years,  especially  such  as 


viii  AGRONOMY 

pertain  to  the  training  of  special  shrubs,  trees,  and  vines,  and 
the  propagation  or  breeding  of  plants.  The  greatest  success 
attends  a  class  in  which  each  pupil  is  allotted  space  for  an 
individual  garden,  though  two  pupils  may  work  in  partner- 
ship with  good  results. 

Every  effort  should  be  made  to  have  the  student  secure 
first-hand  information.  A  single  visit  to  an  implement  store, 
for  instance,  will  give  him  more  information  of  real  value 
than  hours  of  recitation  about  implements  which  he  has  never 
seen  or  examined.  For  the  same  reason  frequent  field  trips 
to  parks,  market  gardens,  nurseries,  greenhouses,  public  gar- 
dens, and  the  like  should  be  made.  These  trips  should,  if 
possible,  be  taken  in  the  hours  allotted  to  agronomy  in  the 
school  day  and  should  be  counted  as  part  of  the  regular 
work.  In  many  cases  the  period  for  this  study  may  come 
last  in  the  day's  program,  thus  allowing  pupils  to  take  as 
much  additional  time  for  the  work  after  school  as  they  desire. 
There  is  always  a  tendency  on  the  part  of  the  teacher  to 
assume  more  knowledge  of  familiar  things  than  the  student 
possesses,  and  for  this  reason  it  is  well  to  carry  out  all  the 
exercises  suggested,  though  at  first  glance  some  may  appear 
too  simple  to  be  worth  while. 

To  the  end  that  the  pupils  be  made  conversant  with  the 
literature  of  the  subject,  they  should  be  encouraged  to  con- 
sult the  reference  works  named  at  the  end  of  each  chapter,  as 
well  as  more  general  works  such  as  Bailey's  "  Cyclopedia  of 
American  Horticulture  "  and  "  Cyclopedia  of  American  Agri- 
culture." Each  student  should  also  be  encouraged  to  write 
to  the  national  government  for  such  publications  on  plants 
as  may  interest  him.  Upon  application,  the  Superintendent 
of  Documents,  Government  Printing  Office,  Washington,  D.  C, 
will  send  a  list  of  publications  to  which  a  price  is  attached, 
and  the  Editor  and  Chief  of  the  Division  of  Publications, 
Department  of  Agriculture,  will  send  a  monthly  list  of  free 


PREFACE  ix 

publications.  In  the  case  of  the  more  expensive  publications 
the  pupil's  representative  in  Congress  or  his  senator  may  se- 
cure them  free.  The  publications  of  his  own  state  agricul- 
tural experiment  station  will  also  be  most  useful,  and  those 
of  other  states  may  often  be  obtained.  All  available  pamphlets 
of  the  kind  should,  of  course,  be  in  the  school  library.  It  is 
often  possible  to  secure  enough  duplicates  of  the  more  impor- 
tant publications  to  allow  one  for  each  member  of  the  class. 
The  pupils  sliould  also  be  supplied  with  the  catalogues  of 
reliable  seedsmen  and  growers  of  nursery  stock.  These  may 
usually  be  liad  upon  request,  and  the  writing  of  a  letter  for 
this  purpose  may  well  be  made  a  part  of  the  class  work. 

At  the  time  the  work  in  agronomy  is  begun  the  weather 
is  not  likely  to  be  favorable  for  work  in  the  open,  but  there 
are,  fortunately,  many  matters  of  theory  and  fact  that  may 
be  discussed  in  the  classroom  before  the  season  for  gardening 
begins,  and  some  of  the  experiments  may  also  be  performed. 
The  book  has  been  arranged,  as  far  as  practicable,  to  follow 
the  progress  of  the  seasons,  but  in  the  early  weeks  of  the 
course  the  theoretical  may  overshadow  the  practical,  and  mat- 
ters may  be  discussed  that  will  not  be  taken  up  in  a  practical 
way  until  much  later.  By  looking  ahead  and  selecting  those 
exercises  that  may  be  performed  as  well  at  one  time  as  at 
another,  the  student  will  be  enabled  to  approach  the  real 
work  of  the  course  with  considerable  theoretical  knowledge 
that  can  be  tested  later  by  practice. 

One  cannot  deal  intelligently  with  plants  without  knowing 
their  names  and  relationships,  and  it  is  recommended  that  the 
identification  of  plants  by  the  use  of  a  good  manual  of  botany 
be  made  part  of  the  course.  For  this  work  the  strictly  tech- 
nical manuals  are  better  than  the  more  popular  volumes,  since 
they  not  only  give  the  names  but  teach  exactness,  increase  the 
vocabulary,  and  familiarize  the  pupil  with  the  use  of  scientific 
keys.   The  small  preliminary  instruction  needed  for  the  use  of 


X  AGRONOMY 

sucli  a  manual  may  be  given  in  the  early  part  of  the  course, 
thus  preparing  the  student  to  name  the  flowers  as  fast  as  they 
appear. 

It  is  not  easy  to  overestimate  the  value  of  all  sorts  of  col- 
lections for  use  in  connection  with  agronomy.  The  accumula- 
tion of  striking  objects  with  which  to  illustrate  the  course  is, 
however,  not  a  matter  of  a  single  year,  for  the  specimens  must 
be  secured  a  few  at  a  time  as  they  are  found.  Soil  maps,  typ- 
ical fungi,  seed  collections,  samples  of  soils  and  fertilizers, 
mineral  specimens  and  pictures  of  unusual  crops,  specimen 
plants,  and  unfamiliar  farming  operations  all  add  to  the  attrac- 
tiveness and  interest  of  the  course.  If  the  school  does  not 
possess  a  museum  in  which  these  may  be  kept,  they  should  be 
carefully  preserved  in  the  laboratory  or  classroom. 

In  most  cases  specific  directions  for  performing  an  experi- 
ment or  for  carrying  on  the  other  work  of  the  course  have 
been  omitted  from  this  book,  since  the  conditions  in  different 
schools  are  likely  to  vary,  and  the  teacher  will  naturally  prefer 
to  work  these  out  to  fit  his  own  local  conditions.  Indeed,  in 
many  instances,  the  planning  of  the  work  may  be  left  to  the 
student.  No  doubt  mistakes  will  be  made,  but  one  may  learn 
much  from  his  mistakes.  If  the  pupils  have  not  had  an  earlier 
course  in  botany,  or  if  it  is  desired  to  go  deeper  into  the  sub- 
ject of  the  organization  of  the  plant  than  is  here  presented, 
the  author's  "  Laboratory  Botany  for  the  High  School "  may 
be  found  useful. 

The  sources  of  the  illustrations  in  this  volume  are  for  the 
most  part  indicated  in  connection  with  the  illustrations  them- 
selves, but  the  author  takes  this  opportunity  to  acknowledge 
his  indebtedness  to  the  Bateman  Manufacturing  Company, 
Greenloch,  New  Jersey ;  Wagner's  Park  Conservatories,  Sid- 
ney, Ohio  ;  The  Lord  and  Burnham  Company,  New  York;  and 
S.  L.  Allen,  Philadelphia,  for  the  loan  of  photographs  and 
other  material.    Several  illustrations  that  originally  appeared 


PREFACE  xi 

in  Duggar's  "  Fungous  Diseases  of  Plants  "  and  Bergen  and 
Caldwell's  "  Practical  Botany "  have  been  secured  through 
the  kindness  of  the  authors  of  these  books.  Other  drawings 
in  the  book  are  the  work  of  the  author's  pupils,  and  the  data 
for  the  tables  of  precipitation  were  supplied  by  Mr.  F.  M. 
Muhlig,  United  States  weather  observer  at  Joliet.  The  author 
is  especially  indebted  to  his  friends,  Mr.  A.  T.  Weaver  of  the 
American  Steel  and  Wire  Company  and  Mr.  Mark  Bennitt  of 
the  H.  L.  Hollister  Land  Company,  Chicago,  for  the  use  of 
numerous  excellent  photographs,  and  to  them,  as  well  as  to 
the  others  mentioned,  he  extends  his  sincere  thanks. 

For  a  careful  reading  of  the  entire  proof  and  for  many  help- 
ful suggestions  in  connection  therewith,  the  author  is  under 
deep  obligations  to  his  colleague.  Professor  E.  F.  Downey  of 
the  Flower  Technical  High  School,  Chicago;  to  Professor  Grant 
Smith,  Chicago  Teachers'  College ;  and  to  Professor  John 
H.  Schaffner,  head  of  the  department  of  botany,  Ohio  State 
University.  To  his  failure  to  adopt  in  some  instances  the  sug- 
gestions made,  must  be  attributed  such  errors  as  may  be  de- 
tected. By  far  the  larger  number  of  drawings  in  the  book  are 
the  work  of  the  author's  wife,  Ida  Martin  Clute,  and  to  her 
he  is  further  indebted  for  invaluable  assistance  in  preparing 
the  text  and  in  correcting  the  proofs. 

WILLARD  X.  CLUTE 
Joliet,  Illinois 


CONTENTS 

PAGE 

CHAPTER  I.   A  LESSON  IN  CHEMISTRY       . 1 

Chemical  elements.  Atoms  and  molecules.  Chemical  formulas. 
Chemical  compounds.  Distribution  of  the  elements.  Elements  found 
in  plants.  Potassium.  Sodium.  Magnesium.  Calcium.  Aluminum. 
Iron.  Manganese.  Oxygen.  Hydrogen.  Nitrogen.  Chlorine, 
Carbon.    Phosphorus.    Sulphur.   Silicon.   Practical  exercises. 

CHAPTER  II.   ORIGIN  OF  THE  SOIL 11 

What  the  soil  is.  Depth  of  the  soil.  The  subsoil.  Origin  of  the  soil 
and  subsoil.  Weathering.  Weathering  by  decomposition.  Weather- 
ing by  disintegration.  Work  of  glaciers.  Modifications  of  the  bed 
rock.   Table  of  rocks.   Changes  in  mantle  rock.    Practical  exercises. 

CHAPTER  III.   TYPES  OF  SOILS 25 

Named  for  their  origin.  Sedentary  soils.  Lacustrine  soils.  iEolian 
soils.  Volcanic  soils.  Colluvial  soils.  Glacial  soils.  Alluvial  soils. 
Soil  constituents.  Sand  and  clay  contrasted.  Loam.  Alkali  soils. 
Acid  soils.  A  test  for  acid  soils.  Artificial  soils.  Practical  exercises. 

CHAPTER  IV.    CONDITIONS  AFFECTING  SOIL  FERTILITY      .     38 

Structure.  The  air.  Air  in  the  soil.  Temperature.  Variations  in 
temperature.  Other  factors  that  modify  temperatures.  The  Fahren- 
heit and  centigrade  scales.  Precipitation.  Water  in  the  soil.  The 
water  table.  Drainage.  Irrigation.  Dry  farming.  Physiologically 
dry  soils.   Practical  exercises. 

CHAPTER  V.  THE  ORGANIZATION  OF  THE  PLANT  ....  55 

The  great  plant  groups.  The  regions  of  the  plant.  Cellular  structure 
of  the  plant.  Roots.  Taproots.  Structure  of  the  root.  Root  hairs. 
Osmosis.  The  stem.  Structure  of  the  stem.  Buds,  Leaves.  Internal 
structure  of  the  leaf.  Formation  of  plant  food.  Transpiration, 
The  flower.  Pollination.  The  fruit.  The  seed.  Life  cycle  of  plants. 
The  rest  period  of  plants.  Genera,  species,  and  varieties.  Scientific 
names.   Practical  exercises. 

xiii 


xiv  AGRONOMY 

PAGE 

CHAPTER  VI.   THE  ELEMENTS  NEEDED  BY  PLANTS     ...     95 

Source  of  the  elements.  Selective  absorption.  Use  of  water  to  the 
plant.  Root  pressure.  Carbon  dioxide.  Nitrogen.  Calcium  and 
magnesium.  Potassium  and  phosphorus.  Sulphur  and  iron.  Chlorine, 
silicon,  and  others.   Practical  exercises. 

CHAPTER  VII.   FERTILIZERS       101 

The  available  mineral  in  the  soil.  Toxic  substances  in  the  soil.  Ele- 
ments that  may  be  lacking.  Sources  of  the  needed  elements.  Manures. 
Green  manures.  Nitrification.  Bacteria  and  nitrification.  Nitrogen 
fixation.  Mycorrhizas.  Soil  inoculation.  Denitrifying  bacteria. 
•  Harmful  organisms  in  the  soil.  Limiting  factors  in  plant  growth. 
Practical  exercises. 

CHAPTER  VIII.    THE    PLANT   IN   RELATION   TO   TEMPERA- 
TURE, LIGHT,  AND  MOISTURE 113 

Growth  temperature.  Hardy  and  tender  plants.  Cardinal  points. 
Acclimatization.  Frost.  Locality  and  frost.  How  cold  kills  plants. 
Other  effects  of  cold.  How  plants  avoid  the  effects  of  cold.  Artifi- 
cial protection  from  the  cold.  Treatment  of  frostbitten  plants. 
Effects  of  heat.  Protection  from  heat.  Need  of  light.  Effects  of 
lack  of  light.  Blanching.  Protection  from  light.  Effects  of  over- 
watering.  Time  to  water.  Effects  of  lack  of  water.  Water  and 
plant  forms.   Practical  exercises. 

CHAPTER  IX.    GARDEN  MAKING 129 

Location  of  the  garden.  Preparing  the  soil.  The  garden  plan.  How 
to  plant.  When  to  plant.  Autumn  seed  bed.  Germination.  Seed  test- 
ing. Double  cropping.  Transplanting.  Inducing  plants  to  fruit. 
Thinning.   Labels.    Saving  seed.  Seed  packets.   Practical  exercises. 

CHAPTER  X.   TILLAGE 149 

Need  for  tillage.  Pulverizing  the  soil.  Mulches.  Work  of  earth- 
worms and  ants.    Rotation  of  crops.   Practical  exercises. 

CHAPTER  XI.   FORCING  AND  RETARDING  PLANTS  ....  157 

Nature  of  the  process.  Retarding.  Greenhouses  and  hothouses.  Hot- 
beds. Cold  frames.  Forcing  single  hills.  Etherization.  Forcing 
plants  in  the  window  garden.    Practical  exercises. 

CHAPTER  XII.    WEEDS 164 

Definition  of  a  weed.  Harmfulness  of  weeds.  Nature  of  weeds. 
Eradicating  weeds.  Purslane.  Spreading  amaranth.  Green  ama- 
ranth.   Tumbleweed.    Pigweed.    Russian  thistle.    Spotted  spurge. 


CONTENTS  XV 

PAGE 

Dandelion.  Plantain.  Common  bindweed.  Black  bindweed.  Prickly 
lettuce.  Ragweed.  Wild  mustard.  Oxeye  daisy.  Canada  thistle. 
Quack  grass.  Crab  grass.  Foxtail.  Old  witch  grass.  Buttercup. 
Wild  carrot.    Sorrel.   Other  weeds.    Practical  exercises. 

CHAITER  XIII.    PROPAGATION 181 

Natural  methods.  Typical  forms  for  propagation.  Artificial  propaga- 
tion. Cuttings.  Hardwood  cuttings.  Layering.  The  sand  box.  Bud- 
ding. Method  of  budding.  Grafting.  Different  forms  of  grafting. 
Inarching.  Grafting  wax.  Effect  of  stock  on  cion.  Practical  exercises. 

CHAPTER  XIV.    DECORATIVE  PLANTING 197 

Purpose.  Lawn  making.  Paths  and  lawn  planting.  Care  of  the 
lawn.  The  border.  Arrangement  of  the  plants.  Shrubs  for  winter 
effects.  Naming  the  shrubs  and  trees.  Herbaceous  plants.  Arrange- 
.  ment  of  herbaceous  perennials.  Hedges.  Bulbs.  Carpet  bedding. 
Formal  planting.  Transplanting  shrubs  and  ti-ees.  Transplanting 
herbaceous  perennials.  Mulching  and  heeling  in.  Treatment  of 
woodlands.    Enemies  of  the  forest.   Practical  exercises. 

CHAPTER  XV.    PRUNING .215 

Purpose  of  pruning.  Time  to  prune.  Pruning  implements.  Methods 
of  pruning.  Making  the  cut.  Specimens  needing  little  pruning. 
Pruning  special  crops.  Thinning.  Heading  in.  Root  pruning.  Gir- 
dling. Cavities  and  broken  limbs.  Topiary  work.  Practical  exercises. 

CHAPTER  XVI.    PLANT  DISEASES        230 

Origin.  Number  of  plant  diseases.  Rots.  Wilts.  Blights.  Leaf  spot. 
Molds  and  mildews.  Smuts.  Rusts.  Wound  parasites.  Other  plant 
diseases.  Sprays  and  spraying.  Bordeaux  mixture.  Lime-sulphur 
wash.  Ammoniacal  copper  carbonate.  Potassium  sulphide  solution.* 
Preventive  measures.   Practical  exercises. 

CHAl'TER  XVII.    INSECT  PESTS        245 

How  insects  injure  plants.  Metamorphoses  of  insects.  Forms  of 
insects  that  cause  injury.  Cutworms.  Cabbage  worm.  Currant 
worm.  Tomato  worm.  Corn-ear  worm.  Tent  caterpillar.  Codlin 
moth.  Curculio.  Cankerworms,  Borers.  Elm-leaf  beetle.  Cucumber 
beetle.  Blister  beetles.  Potato  beetle.  May  beetles.  Plant  lice,  or 
aphids.  Squash  bug.  Mealy  bug.  Scale  insects.  Preventing  attacks 
of  insects.  Poisons  for  chewing  insects.  Remedies  against  sucking 
insects.  Spray  pumps.  Other  aids  in  fighting  insects.  Practical 
exercises. 


xvi  AGRONOMY 

PAGE 

CHAPTER  XVIII.   PLANT  BREEDING        258 

Need  for  breeding.  Basis  for  breeding.  Inducing  variation.  Hybrids 
and  hybridizing.  Producing  the  cross.  Mendel's  law.  Selection. 
Roguing.   Xenia.   Parthenogenesis.   Practical  exercises. 

CHAPTER  XIX.   THE  ORIGIN  OF  SPECIES 272 

Evolution.  Struggle  for  existence.  Natural  selection.  Results  of 
variation.  Darwinian  theory.  Mutation  theory.  Practical  exercises. 

CHAPTER  XX.    OUR  CULTIVATED  PLANTS 277 

Origin.  Edible  parts  of  plants.  Root  crops.  Leaf  crops.  The 
legumes.  Solanaceous  fruits.  Gourd  fruits.  The  grasses.  Bush 
fruits.   Tree  fruits.   New  fruits.   Practical  exercises. 

APPENDIX 

Seventv-five  Shrubs  Useful  for  Planting 285 

Fifteen  Woody  Vines  Desirable  for  Arbors  and  Porches      .  288 
Fifty  Desirable  Herbaceous  Perennials 289 

INDEX 291 


AGRONOMY 

CHAPTER  I 

A  LESSON  IN  CHEMISTRY 

Chemical  elements.  The  earth's  crust,  the  animals  and 
plants  upon  it,  and  the  multitude  of  substances  with  which 
we  are  familiar  are  composed  of  a  small  number  of  simpler 
forms  of  matter,  known  as  chemical  elements,  combined  in 
various  ways.  A  chemical  element  may  be  defined  as  a  sub- 
stance that  has  not  been  resolved  into  simpler  substances,  and 
as  thus  defined  there  are  only  about  eighty  chemical  elements 
in  the  world.  Gold  may  be  taken  as  an  illustration.  Though 
it  be  divided  into  particles  too  small  to  be  visible  in  the 
microscope,  or  heated  until  it  becomes  liquid,  or  subjected  to 
strong  currents  of  electricity,  it  is  still  gold  and  nothing  else. 
A  few  chemical  elements  may  be  found  "  native,"  that  is, 
uncombined  with  others,  but  usually  two  or  more  unite  to 
form  chemical  compounds.  By  far  the  larger  number  are  always 
found  thus  combined.  Oxygen  may  be  cited  as  a  familiar 
example  of  an  element  that  exists  both  free  and  combined. 
As  a  free  gas  it  forms  about  one  fifth  of  the  air  we  breathe ; 
combined  with  other  elements  it  makes  up  about  half  of  the 
water  and  rock  of  the  earth's  crust.  Chemical  elements  are 
often  grouped  as  metals  and  nonmetals,  the  metals  being 
greatly  in  the  majority.  Usually  the  metals  may  be  distin- 
guished by  names  ending  in  um.  The  diiTerence  between  a 
metal  and  a  nonmetal,  however,  is  not  easily  defined.  A 
metal  is  supposed  to  have  the  following  properties :  it  must 

1 


2  AGRONOMY 

exist  as  a  solid  and  have  a  metallic  luster,  must  be  capable 
of  conducting  heat  and  electricity,  must  be  opaque,  hard, 
malleable,  ductile,  and  capable  of  forming  compounds  with 
oxygen.  Probably  no  single  metal  has  all  these  properties, 
but  no  substance  would  be  accepted  as  a  metal  that  did  not 
possess  many  of  them.  Iron,  nickel,  copper,  and  mercury  are 
among  the  more  familiar  metals.  Carbon,  sulphur,  and  phos- 
phorus may  be  named  as  examples  of  the  nonmetals.  Theo- 
retically, at  least,  each  chemical  element  may  exist  as  a  solid, 
a  liquid,  or  a  gas,  but  many  have  not  yet  been  produced  in  all 
three  of  these  conditions.  Increasing  the  temperature  will 
make  many  of  the  ordinary  solids  liquid,  and  the  reverse  of 
this  process,  combined  with  pressure,  serves  to  liquefy  even 
the  lightest  gases.  Water,  while  not  a  chemical  element,  will 
serve  to  illustrate  this  change  of  state.  In  its  more  familiar 
form  it  is  a  liquid,  but  if  heated  to  212°  F.  it  becomes  a 
gas,  and  if  cooled  below  32°  F.  it  becomes  a  solid. 

Atoms  and  molecules.  An  atom  is  the  smallest  part  of  a 
chemical  element  that  can  enter  into  combination  with  other 
parts.  Atoms  may  therefore  be  said  to  be  the  units  of  which 
more  complex  compounds  are  built.  Not  very  much  is  known 
regarding  the  size  of  atoms,  but  they  are  estimated  to  be 
about  one  hundred-millionth  of  an  inch  in  diameter  and  to 
bear  about  the  same  relation  to  the  size  of  a  tennis  ball  that 
the  latter  bears  to  the  earth.  Atoms  usually  do  not  long 
exist  as  such,  but  combine  with  other  atoms  to  form  molecules^ 
which  are  the  smallest  enduring  particles  of  a  compound,  just 
as  the  atoms  are  the  smallest  part  of  a  chemical  element.  All 
the  atoms  of  a  single  chemical  element  are  exactly  alike, 
otherwise  it  would  not  be  a  chemical  element. 

Chemical  formulas.  Atoms  have  the  same  relation  to  chemi- 
cal compounds  that  letters  have  to  words,  and  the  chemist  is 
therefore  able  to  write  a  definite  formula  for  the  molecule  of 
every  substance.    Each  element  has  its  own  chemical  symbol, 


A  LESSON  IN  CHEMISTRY  3 

usually  the  initial  of  its  name,  as  C  for  carbon  and  P  for 
phosphorus.  When  the  initial  is  duplicated  in  the  list  of 
symbols,  one  more  distinguishing  letter  may  be  added,  as 
Ca  for  calcium  and  Pt  for  platmum.  Occasionally  an  element 
may  be  given  the  initial  of  an  older  name,  as  in  the  case  of  K 
for  potassium,  where  the  initial  stands  for  kalium.  Iron  has 
the  symbol  Fe,  derived  from  ferrtim.  The  student  familiar 
with  the  names  of  the  elements  readily  recognizes  the  kinds 
of  atoms  that  form  a  given  compound  when  its  formula  is 
read.  When  more  than  one  atom  of  a  kind  enters  into  the 
combination,  the  number  is  written  below  the  line  and  im- 
mediately following  the  symbol.  Thus  the  formula  CO^, 
representing  a  molecule  of  carbon  dioxide,  is  seen  to  consist  of 
one  atom  of  carbon  united  with  two  atoms  of  oxygen.  The 
molecule   of  water  is  written   H^O.    In   this   two   atoms   of 

Table  of  the  More  Common  Chemical  Elements 


Name 

Aluminum     .     . 
Antimony  (^slibium) 

Argon 

Arsenic  .... 
Barium  .  .  .  . 
Bismuth    .     .     .     . 

Boron 

Bromine  .  .  .  . 
Calcium  .  .  .  . 
Carbon  .  .  .  . 
Chlorine  .  .  .  . 
Cobalt  .  .  .  . 
Copper  (cuprum) 
Fluorine  .... 
Gold  (aurum)  .  . 
Hydrogen 

Iodine 

Iron  (ferrum)     . 


Symbol 


Al 

Sb 

A 

As 

Ba 

Bi 

B 

Br 

Ca 

C 

CI 

Co 

Cu 

F 

Au 

H 

I 

Fe 


Lead  (plumhum)  . 
Lithium 
Magnesium 
Manganese 
Mercury  (Jiydraiujjjruin) 
Nickel     .... 
Nitrogen 
Oxygen  .... 
Phosphorus      .     . 
Platinum     . 
Potassium  (kalium) 
Silicon    .... 
Silver  (aryetilum) 
Sodium  (^natrium) 
Sulphur  .... 
Tin  (niannum) 
Tungsten  (icol/ram) 
Zinc 


Symbol 


Pb 

Li 

Mg 

Mn 

Hg 

Ni 

N 

O 

P 

Pt 

K 

Si 

Ag 

Na 

S 

Sn 

W 

Zn 


4  AGRONOMY 

hydrogen  are  joined  to  one  of  oxygen.  When  symbols  in 
parentliesis  are  followed  by  a  number  written  below  the  line, 
as  Ca(NOg).,,  it  signifies  that  the  elements  and  quantities  in 
parenthesis  are  to  be  multiplied  by  the  number  so  written. 
Calcium  phosphate  (Cag(PO^).^  would  also  be  correctly 
written  CagP^O^. 

Chemical  compounds.  When  salt  and  sand,  or  charcoal  and 
sulphur,  are  stirred  up  together,  the  result  is  a  mere  mechan- 
ical mixture.  In  a  chemical  compound  an  entirely  new  sub- 
stance is  formed,  which  may  possess  characteristics  quite  unlike 
those  of  the  combining  elements.  Under  certain  conditions 
charcoal  and  sulphur  may  be  made  to  form  a  chemical  union 
in  which  two  atoms  of  sulphur  join  with  one  of  carbon  to  pro- 
duce carbon  disulphide  (CS^).  Sulphur,  as  everybody  knows, 
is  a  yellow  solid  and  carbon  a  black  solid,  but  the  carbon 
disulphide  formed  by  their  union  is  neither  black,  yellow,  nor 
a  solid,  but  is  a  colorless  liquid  resembling  water.  Moreover, 
while  either  pure  carbon  or  sulphur  may  be  eaten  without 
harm,  when  they  are  chemically  combined  they  form  a  deadly 
poisonous  liquid,  which,  exposed  to  the  air,  soon  turns  to  a 
heavy,  suffocatmg,  and  highly  inflammable  gas.  Again,  when 
carbon  is  burned  in  the  air,  as  in  ordmary  wood  and  coal  fires, 
one  atom  of  carbon  unites  with  two  of  oxygen  and  forms  a 
colorless,  suffocating  gas  known  as  carbon  dioxide  (CO^).  In 
a  similar  way  sulphur  may  be  burned  to  form  sulphur  dioxide 
(SO.,).  Calcium  carbide,  from  which  acetylene  gas  is  produced, 
is  another  union  of  carbon  and  is  represented  by  the  formula 
CaC^.  It  is  interesting  to  note  that  all  the  chemical  elements 
unite  with  others  in  definite  and  unvarying  proportions.  No 
matter  how  much  oxygen  may  be  present  when  carbon  is 
burned,  the  molecule  of  carbon  dioxide  formed  always  consists 
of  two  atoms  of  oxygen  and  one  of  carbon.  Carbon,  however, 
may  be  made  to  form  other  combinations  with  oxygen.  When 
there  is  a  lack  of  oxygen,  carbon  monoxide  (CO)  may  be 


A  LESSON  m  CHEMISTRY  6 

formed.  Some  elements,  oxygen  and  carbon  for  instance, 
readily  combine  with  a  great  many  others,  while  some,  like 
nitrogen  and  argon,  are  called  inert,  and  only  with  difficulty 
can  be  made  to  unite  with  others.  In  chemical  reactions  heat 
is  often  evolved.  A  good  illustration  of  this  is  seen  in  the 
heat  that  results  from  the  union  of  oxygen  and  carbon  when 
wood  or  coal  is  burned,  or  when  water  is  added  to  quicklime 
in  the  process  of  making  mortar. 

Distribution  of  the  elements.  The  different  elements  are  very 
unequally  distributed.  Some,  like  radium,  are  found  in  very 
minute  quantities  and  always  in  combination  with  other  ele- 
ments, while  others  may  form  vast  deposits  which  are  nearly 
pure.  Only  about  forty  of  the  elements  are  at  all  common, 
while  but  five  of  these  form  96  per  cent  of  the  planet  on  which 
we  live.  These  five  in  the  order  of  their  abundance  are  oxygen, 
silicon,  aluminum,  iron,  and  calcium.  Since  the  soil  consists 
of  particles  from  many  kinds  of  rocks,  it  contains  a  consider- 
able number  of  chemical  elements,  but  only  sixteen  that  are 
at  all  abundant,  namely,  oxygen,  silicon,  carbon,  sulphur, 
hydrogen,  chlorine,  phosphorus,  fluorine,  aluminum,  calcium, 
magnesium,  potassium,  sodium,  iron,  manganese,  and  barium. 

Elements  found  in  plants.  Fifteen  of  the  sixteen  connnon 
chemical  elements  in  the  soil  are  found  in  plants.  Of  these, 
seven  are  metals  and  eight  are  nonmetals.  In  the  first  group 
are  potassium,  sodium,  magnesium,  calcium,  aluminum,  iron, 
and  mangau^ie  ;  m  the  second  are  oxygen,  hydrogen,  nitrogen, 
chlorine,  caPBhf  phosphorus,  sulphur,  and  silicon.  Several  of 
these  are  not  regarded  as  essential  to  plant  growth,  as  is  also 
true  of  litliium,  zmc,  copper,  boron,  and  fluorine,  which  are 
occasionally  found  in  plants  in  certain  regions.  Some  of  the 
characteristics  of  the  fifteen  elements  usually  found  in  plants 
are  given  below. 

Potassium  (K)  is  a  soft  white  metal,  lighter  than  water.  It 
quickly  oxidizes  or  unites  with  oxygen  when  exposed  to  the 


6  AGRONOMY 

air,  and  must  be  kept  in  oil  or  other  substances  that  do  not 
contain  oxygen.  It  does  not  occur  in  the  free  state,  but  is 
always  combined  with  other  elements,  as  carbonates,  sulphates, 
silicates,  and  chlorides.  Potash  is  an  oxide  of  potassium,  and 
feldspar  and  mica  consist  largely  of  this  element.  Potassium 
is  present  in  the  ash  of  all  plants,  is  found  most  abundantly 
in  the  growing  parts,  and  is  essential  to  plant  life. 

Sodium  (Na)  is  a  soft,  waxy,  lustrous  white  metal  much  like 
potassium  in  appearance  and  always  occurs  combined  with 
other  elements.  It  oxidizes  even  in  water  and  must  be  kept 
in  fluids  lacking  oxygen.  Its  various  combinations  are  abun- 
dant in  the  rocks.  Sodium  chloride  (NaCl)  is  rock  salt.  What 
we  commonly  call  soda  is  an  oxide  or  carbonate  of  sodium. 
Chile  saltpeter,  or  nitrate  of  soda,  is  largely  used  as  a  fertilizer. 
Sodium,  while  usually  found  in  plants,  is  known  to  be  non- 
essential, though  it  may  take  the  place  of  potassium  in  neutral- 
izing some  of  the  acids  formed  in  them.  The  chemical  symbol  is 
taken  from  natrium,  the  name  by  which  it  was  formerly  known. 

Magnesium  (Mg)  is  a  light,  silvery  white,  moderately  hard 
metal  which  is  malleable  but  not  very  tenacious.  It  is  not 
found  native,  but  forms  many  compounds.  It  is  permanent  in 
dry  air,  but  tarnishes  in  the  presence  of  moisture.  Burned  in 
oxygen,  it  produces  a  blinding  light  and  forms  magnesium 
oxide  (MgO),  or  magnesia.  Dolomite  and  asbestos  contain 
much  magnesium,  and  Epsom  salts  is  the  sulphate  of  this 
element.  Magnesium  is  found  in  most  parts  of^j^  plant,  but 
less  abundantly  than  calcium,  except  in  tHWB^s,  where  it 
is  usually  more  abundant. 

Calcium  (Ca)  is  a  pale  yellow,  malleable,  ductile,  but  some- 
what brittle,  metal.  It  is  widely  distributed,  but  never  free. 
It  is  the  chief  element  in  marbles,  limestones,  and  dolomites. 
Limestone  is  calcium  carbonate  (CaCOg),  and  when  carbon  diox- 
ide is  driven  off  by  burning,  quicklime  (CaO),  which  is  used 
in  plastering,  is  left.    Gypsum  is  calcium  sulphate  (CaSO^). 


A  LESSON  IN  CHEMISTRY  7 

Plaster  of  Paris  is  derived  from  gypsum  by  burning.  The  rock 
called  apatite  contains  large  amounts  of  calcium  phosphate. 
Calcium  is  one  of  the  elements  essential  to  plant  life.  It  is 
posed  to  neutralize  the  acids  that  would  otherwise  injure  the 
plant,  as  well  as  to  play  an  important  part  in  the  production 
of  new  tissues.  Some  plants,  such  as  clover,  beans,  and  peas, 
are  often  called  lime  plants  because  they  require  so  much  of 
this  element  for  their  proper  development. 

Aluminum  (Al)  is  another  of  the  white  metals  that  is  never 
found  native,  though  it  is  the  principal  constituent  of  every 
clay  bank  and  forms  one  twelfth  of  the  earth's  crust.  It  is 
malleable  and  ductile  and  does  not  oxidize  in  the  air.  Clays 
and  feldspars  are  silicates  of  aluminum,  and  the  ruby,  emerald, 
oriental  amethyst,  and  sapphire  are  crystalline  forms  of  the 
same  metal  combined  with  oxygen.  Corundum,  or  emery,  is 
an  impure  crystalline  form.  Though  the  metal  itself  is  soft, 
the  crystalline  forms  are  exceeded  in  hardness  by  the  diamond 
only.  Alum  is  a  combination  of  sulphur  and  potassium  with 
aluminum.  Aluminum  is  usually  found  in  plants,  though  it 
forms  no  part  of  the  plant  food. 

Iron  (Fe)  is  too  well  known  to  need  description.  It  is  abun- 
dant and  widely  distributed,  occurring  usually  as  carbonates 
and  oxides.  It  is  an  ingredient  in  practically  all  soils  and 
forms  about  one  fifteenth  of  the  earth's  crust.  Iron  rust 
and  the  ochers  are  oxides  of  iron,  and  it  is  these  substances 
which  give^ie  red  and  yellow  colors  to  certain  soils.  Iron 
is  essentiaHBltplants.  Its  presence  is  necessary  for  the 
formation  of  chlorophyll,  the  green  color  of  plants,  though, 
so  far  as  known,  it  does  not  enter  into  the  composition  of 
the  color. 

Manganese  (Mn)  is  a  hard,  grayish-white  metal  that  is  fused 
with  difficulty,  but  readily  oxidizes.  While  often  found  in 
plants,  it  has  been  proved  that  it  is  not  necessary  to  their 
growth. 


8  AGROJfOMY 

Oxygen  (0)  at  ordinary  temperatures  is  a  colorless,  odor- 
less gas.  It  is  the  most  abundant  of  the  elements,  forming  as 
it  does  one  fifth  of  the  air,  eight  nmths  of  the  water,  and 
about  one  half  of  the  rocks  and  soil.  It  combines  with  a  great 
number  of  other  elements,  forinuig  oxides,  and  is  necessary 
for  all  ordinary  combustion  and  for  the  respiration  of  animals 
and  plants.  With  hydrogen  and  carbon  it  forms  tlie  carbo- 
hydrates, of  which  the  greater  part  of  the  plant  body  consists. 
Iron  and  other  metals  bum  in  pure  oxygen. 

Hydrogen  (H)  is  a  colorless,  tasteless,  and  odorless  gas,  and 
is  the  lightest  substance  known.  It  does  not  occur  free,  but 
is  most  abundant  combined  with  oxygen  in  the  form  of  water. 
It  burns  with  a  blue  flame  and  is  a  constituent  of  all  acids. 
Hydrogen  and  oxygen,  if  mixed  at  ordinary  temperatures, 
will  remain  a  mere  mixture,  but  if  heated  or  ignited  they 
combine  with  a  violent  explosion  and  form  water. 

Nitrogen  (N)  is  a  heavy,  inert,  colorless,  tasteless,  odorless 
gas  that  occurs  free  in  the  air,  of  which  it  forms  about  four 
fifths.  It  is  extremely  inert,  does  not  support  combustion,  nor 
readily  enter  into  combination  with  other  elements.  It  is  four- 
teen times  as  heavy  as  hydrogen,  and  without  it  the  air  would 
have  little  weight,  birds  could  not  fly,  and  the  sails  of  ships 
and  windmills  would  be  practically  useless.  Nitrogen  also 
serves  to  dilute  the  oxygen  in  the  air;  otherwise  oxidation 
in  our  bodies  would  proceed  so  rapidly  as  to  be  harmful. 
Ammonia  gas  is  largely  nitrogen,  and  gunpomler,  guncot- 
ton,  and  nitroglycerin  owe  their  effectivenesiRJPlhe  fact  that 
these  are  unstable  compounds  containing  this  element.  Nitro- 
gen does  not  exist  in  the  mineral  matter  of  the  earth,  though 
the  soil  is  the  source  of  most  of  this  element  used  by  plants. 
Here  it-  exists  largely  in  the  form  of  nitrates  derived  from  the 
decaying  organic  matter.  Nitrogen  is  necessary  to  the  formation 
of  proteins  and  is  an  essential  constituent  of  the  protoplasm  of 
all  animals  and  plants. 


A  LESSON  m  CHEMISTRY  9 

Chlorine  (CI)  is  a  heavy,  yellow-green,  poisonous  gas,  with  a 
disagreeable,  suffocating  odor.  It  is  never  found  free,  but  is 
widely  distributed  in  nature  in  compounds,  the  most  familiar 
of  which  is  common  salt  (NaCl).  Chlorine  apparently  takes 
no  part  in  the  life  processes  of  plants,  but  is  common  m  the 
compounds  used  by  them. 

Carbon  (C)  is  a  black  solid,  familiar  to  us  in  charcoal  and 
mineral  coal.  Graphite,  or  black  lead,  used  in  pencils,  is 
another  form  of  this  element.  The  diamond,  the  hardest  sub- 
stance known,  is  a  crystalline  form  of  carbon.  Peat  and  muck 
are  impure  forms.  Carbon  has  never  been  liquefied,  but  it 
may  be  turned  to  a  gas  at  very  high  temperatures ;  many  of 
its  compounds  are  gases  or  liquids  at  ordinary  temperatures. 
When  carbon  unites  with  oxygen,  heat  and  light  result.  In 
slow  combustion,  such  as  that  in  our  bodies,  no  light  is  pro- 
duced, but  the  amount  of  heat  that  finally  results  is  the 
same  as  if  the  substances  burned  more  rapidly.  The  carbon 
so  abundant  in  plants  is  not  derived  from  the  soil,  but  from 
the  small  quantity  of  carbon  dioxide  in  the  air.  Carbon  is 
believed  to  occur  in  more  different  compounds  than  any 
other  element. 

Phosphorus  (P)  is  a  pale  yellow,  poisonous  substance  about 
as  soft  as  wax  and  has  a  disagreeable  odor.  It  does  not  occur 
native,  but  in  such  combinations  as  phosphates  of  lime  and 
aluminum  it  is  present  in  large  quantities  in  many  rocks. 
It  burns  with  a  yellow-white  light  when  exposed  to  the  air, 
and  must  be  kept  under  water  in  the  laboratory.  Phosphorus 
is  a  necessary  constituent  of  the  nucleus  of  plant  and  animal 
cells  and  is  also  found  in  considerable  abundance  in  seeds. 

Sulphur  (S)  is  a  yellow  substance  occurring  native  or  com- 
bined with  various  elements,  as  sulphates  and  sulphides.  It 
melts  readily,  and  burns  with  a  bluish  flame  and  suffocating 
odor,  producing  sulphur  dioxide  (SO^).  Sulphur  is  an  essen- 
tial element  in  all  plant  and  animal  bodies. 


10  AGRONOMY 

Silicon  (Si)  when  pure  consists  of  lustrous  brown  or  black 
crystals,  but  it  does  not  exist  in  nature  uncombined.  Next  to 
oxygen  it  is  the  most  widely  distributed  of  the  elements  and 
forms  one  fourth  of  the  earth's  crust.  In  combination  with 
oxygen,  silicon  forms  the  clear  and  glasslike  mineral  quartz 
(SiOj),  and  is  thus  the  principal  element  in  sand.  From  60 
to  90  per  cent  of  most  soils  is  quartz. 

PRACTICAL  EXERCISES 

1.  Look  over  the  list  of  chemical  elements  given  on  page  3  and 
name  those  possessed  by  the  class  in  the  shaj^  of  jewelry,  coins,  etc. 

2.  Make  a  list  of  these  and  of  the  others  that  may  be  found  in  the 
schoolroom. 

3.  Visit  the  chemistry  department  of  the  school,  or  the  nearest  drug 
store,  and  list  any  other  uncombined  elements  that  you  may  find. 

4.  In  the  laboratory,  by  appropriate  experiments,  make  carbon  diox- 
ide, sulphur  dioxide,  magnesium  oxide,  etc. 

5.  Pick  out  the  chemical  elements  in  the  following  combinations : 
orthoclase  (KAlSi30g),carnallite  (KClMgC'US  HgO), common  salt  (XaCl), 
Epsom  salts  (MgSO^),  copperas  (FeSO^),  nitric  acid  (HXOg). 

6.  Burn  a  piece  of  limestone  to  drive  off  the  COg,  leaving  quicklime 
(CaO).  Add  water  to  a  piece  of  quicklime  to  make  calcium  hydroxide 
and  note  the  heat  developed  by  the  chemical  reaction. 

7.  Boil  some  water  in  a  Florence  flask  and  watch  the  space  above  the 
boiling  water.    What  is  the  color  of  the  gas  (steam)? 

8.  Watch  the  bubbles  of  gas  rising  from  any  water  plant  when  in 
sunlight.  Catch  some  of  it  by  sinking  a  short-stemmed  glass  funnel 
into  the  water  over  the  plants,  with  the  stem  just  below  the  surface, 
and  inverting  over  it  a  test  tube  filled  with  water.  The  gas  will  rise 
and  displace  the  water  in  the  tube  and  may  be  tested  with  a  glowing 
splinter. 

References 

Hopkins,  "  Soil  Fertility  and  Permanent  Agriculture." 
Snyder,  "Chemistry  of  Plant  and  Animal  Life." 


CHAPTER  II 

ORIGIN  OF  THE  SOIL 

What  the  soil  is.  All  ordinary  plants  are  rooted  in  the  soil, 
which  serves  them  as  a  source  of  food  materials  and  affords  a 
convenient  place  of  anchorage.  The  soil,  however,  is  far  from 
being  the  simple  collection  of  rock  fragments  that  it  is  often 
supposed  to  be.  Fragments  of  rock  are  important,  to  be  sure, 
and  in  orduiary  soils  form  from  60  to  95  per  cent  of  their 
weight ;  but  any  good  agricultural  soil  must  contain,  in  addi- 
tion, air,  water,  humus,  bacteria,  and  similar  organisms.  So 
important  are  all  of  these  that  none  can  be  omitted  without 
impairing  the  fertility  of  the  land.  From  the  rock  fragments 
come  all  the  minerals  used  by  plants.  These  are  steadily, 
though  very  slowly,  dissolved  out  by  the  soil  water  and  carried 
in  solution  into  the  plant.  The  humus,  formed  of  decaying 
plant  and  animal  remains,  is  the  principal  source  of  the  all- 
important  nitrogen ;  but  since  the  plants  cannot  use  it  as 
humus,  it  must  first  be  worked  over  into  nitrates  by  the 
bacteria.  The  higher  plants  are  so  dependent  upon  the  good 
offices  of  tlie  bacteria  in  this  respect  that  if  the  latter  should 
all  disappear  from  the  soil,  crops  would  soon  be  unable  to 
grow  in  it.  The  air  in  the  soil  is  required  for  the  activities 
of  the  bacteria,  as  well  as  for  the  respiration  of  the  under- 
ground parts  of  the  plants. 

Depth  of  the  soil.  The  soil  ranges  from  a  few  inches  to  many 
feet  in  depth.  In  humid  regions  —  that  is,  in  regions  of  abun- 
dant rainfall  —  the  decaying  humus  gives  it  a  darker  color  and 
enables  us  to  distinguish  it  from  the  underlying  materials  ;  but 
in  arid  regions,  where  the  rainfall  is  scanty,  the  humus  is 

11 


12  AGRONOMY 

destroyed  almost  as  fast  as  made,  and  no  such  difference  in 
color  may  be  seen  except  in  the  occasional  low,  wet  lands. 
The  soil  in  arid  lands,  however,  is  often  more  fertile  than  that 
of  humid  regions  and  can  be  cultivated  to  a  greater  depth. 
This  is  mamly  because  the  scanty  rainfall  has  not  washed  out 
and  carried  away  the  food  materials  in  it.  Such  soils  need 
only  to  be  irrigated  to  give  abundant  crops. 

The  subsoil.  The  soil  is  commonly  regarded  as  extending 
downward  as  far  as  traces  of  organic  matter  or  humus  are 
found.  In  humid  regions  this  is  from  a  few  inches  to  several 
feet.  Below  this  is  the  subsoil,  lighter  in  color,  more  compact, 
and  consisting  almost  entirely  of  rock  fragments.  It  is  there- 
fore little  adapted  to  growing  crops,  though  rich  in  the  mate- 
rials needed  by  plants.  While  not  of  itself  able  to  produce 
good  crops,  it  forms  a  storehouse  of  food  materials  upon  which 
the  plant  can  draw,  and,  slowly  breaking  down  under  the  at- 
tacks of  wind  and  weather,  gradually  becomes  part  of  the 
soil  itself. 

Origin  of  the  soil  and  subsoil.  If  one  digs  down  far  enough 
anywhere  on  the  earth,  he  comes  at  last  to  the  solid  rock. 
This  is  called  bed  rock.  Here  and  there  it  comes  to  the  sur- 
face, forming  outcrops,  such  as  may  be  seen  in  the  cliffs  of 
broken  country  or  where  a  rapid  stream  has  cars'^ed  out  a 
deep  valley.  Usually,  however,  it  is  buried  under  a  thick 
deposit  of  rock  fragments,  called  mantle  rock,  which  has  been 
derived  from  the  bed  rock  in  various  ways.  Sections  of  man- 
tle rock  may  be  seen  in  railway  cuts,  gravel  pits,  brickyards, 
and  the  openings  for  quarries  and  mines.  Since  the  bed  rocks 
range  from  soft  and  porous  sandstones  and  limestones  to 
compact  and  flinty  granites,  the  mantle  rock  may  differ  in 
composition  according  to  the  locality,  and  the  soil  derived 
from  the  mantle  rock  necessarily  partakes  of  the  same  char- 
acteristics. Soils  derived  directly  from  the  underlying  bed 
rock  are  known  as  residual  or  sedentary  soils ;  those  brought 


ORIGIN  OF  THE  SOIL  13 

irom  a  distance  by  running  water  or  other  means  are  called 
drift  or  transported  soils. 

Weathering.  The  agencies  that  have  served  to  break  up  the 
bed  rock  into  mantle  rock  and  the  mantle  rock  into  soil  are 
grouped  under  the  general  title  of  weathenng  agencies.  Two 
phases  of  weathering  may  be  distinguished,  namely,  weather- 
ing by  decomposition  and  weathering  by  disintegration.  The 
first  is  largely  a  chemical  process  in  which  some  or  all  of 


if^K"\'f^ 

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1 

Fig.  1.   An  outcrop  of  limestone  showing  weathering 

the  minerals  in  the  rock  are  resolved  into  their  simpler  com- 
pounds, resulting  in  very  fine  particles ;  the  second  is  largely 
a  mechanical  or  grinding  process  and  the  resulting  particles 
are  usually  larger. 

Weathering  by  decomposition.  Air  and  water  are  the  chief 
elements  that  are  effective  in  decomposition.  The  oxygen  in 
the  air  readily  enters  into  combination  with  other  elements  in 
the  rocks  and  soon  tears  down  the  surface  layers  exposed  to 
it,  forming  new  compounds.  Results  of  this  process  are  seen 
in  the  rusting  of  iron  and  the  dulling  of  nearly  all  surfaces 
exposed  to  the  air  for  any  length  of  time.    In  the  quarry  we 


14  AGRONOMY 

readily  distinguish  the  newly  quarried  blocks  from  older  ones, 
by  their  fresh  look.  The  carbon  dioxide  in  the  air  unites  with 
water  to  form  carbonic  acid,  and  this  also  attacks  various 
elements  m  the  rocks  and  tears  them  from  their  compounds. 

Water  breaks  up  the  rocks  by  dissolving  out  the  more 
soluble  compounds.  Pure  water  wears  the  rock  very  slowly, 
but  when  it  contains,  as  it  often  does,  carbon  dioxide  or 
other  acids  derived  from  the  humus  or  the  roots  of  plants, 


Fig.  2.   Underground  channel  in  limestone  made  by  water,  Juliet,  Illinois 
A  iX)rtion  of  the  rock  has  been  dissolved  and  carried  away 

it  is  a  most  powerful  agent  in  weathering.  Limestones,  espe- 
cially, are  quickly  dissolved  by  such  means,  and  the  occur- 
rence of  caves  and  underground  channels  in  these  rocks  is 
thus  explained.  Here  and  there  water  charged  with  dissolved 
minerals  may  come  to  the  surface  and  we  then  have  min- 
eral springs.  Sandstones,  though  usually  more  enduring  than 
limestones,  are  often  rapidly  disintegrated  by  having  the  ma- 
terials which  bind  the  sand  grains  together  dissolved.  Rain 
water  usually  contains  small  amounts  of  ammonia  and  nitric 
acid,  and  these,  like  the  carbonic  acid,  ai-e  active  in  dissolving 


OKIGIN  OF  THE  SOIL 


15 


the  rocks.  The  weathering  effects  of  water  are  not  confined 
to  a  layer  near  the  surface,  as  in  decomposition  by  the  air, 
but  extend  downward  as  far  as  the  water   can   penetrate. 


Photograph  by  H.  L.  Ilollister  Land  Co. 

Fig.  3.   A  deep  valley  in  Colorado,  excavated  mainly  by  running  water 

Not  only  does  the  water  dissolve  the  rocks,  but  it  carries 
the  dissolved  materials  away  to  be  deposited  elsewhere  when 
the  water  evaporates,  thus  building  up  in  one  place  what  it 
tears  down  in  another.  In  this  way  the  stalactites  and  stalag- 
mites found  in  limestone  caves  are  formed,  and  our  beds  of 
rock  salt,  gypsum,  and  bog  nons  are  due  to  the  same  process. 


16 


AGRONOMY 


A  cubic  mile  of  ordinary  river  water  has  been  estimated  to 
contain  about  a  quarter  of  a  million  tons  of  rock  constituents. 
It  is  not  difficult  to  understand,  then,  that  in  many  soils  formed 
by  the  decomposition  of  limestone  rock,  a  layer  of  limestone 
nearly  a  hundi'ed  feet  thick  may  have  been  removed  for  every 


II.  L.  Uollister  Land  Co. 


Fig.  4.   Twin  Falls,  Idaho 


Here  the  Snake  River  has  worn  a  channel  hundreds  of  feet  deep  in 
hard  igneous  rock 

foot  of  soil  left.  In  contrast  to  this,  water,  under  certain  con- 
ditions, instead  of  decreasing  the  bulk  of  the  soil  in  weathering, 
may  actually  increase  it  by  entering  in  combination  with  some 
of  the  elements  in  the  rocks.  Thus  granitic  rocks  in  turning 
to  arable  soil  may  be  increased  in  bulk  more  than  80  per  cent. 
Weathering  by  disintegration.  By  disintegration  the  rocks 
are  broken  up  into  small  pieces  like  the  original  rock  and 
suffer  little,  if  any,  chemical  change.    In  this  process  heat. 


OKIGIN  OF  THE  SOIL 


17 


cold,  and  gravity,  and  water  influenced  by  these  forces,  are 
the  important  agents.  Variations  in  temperature  have  a 
greater  effect  in  weathering  than  is  commonly  supposed. 
Under  the  rays  of  the  noonday  sun,  exposed  rocks  rapidly 
rise  in  temperature  and  expand;  at  night  they  as  rapidly 
cool   and   contract.    This    alternate    heating    and  cooling  is 


Photograph  by  U.  L.  HoUister  Laud  Co. 

Fig.  5.    A  crest  in  the  Rocky  Mountains  showing  rock  fragments 
split  off  by  alternating  heat  and  cold 


frequently  sufficient  to  cause  the  splitting  off  of  large  flakes 
weighing  many  pounds,  with  reports  like  pistol  shots.  The 
different  minerals  in  the  rocks  have  their  own  rate  of  expan- 
sion and  contraction,  and  if  these  varying  movements  under 
changes  of  temperature  do  not  cause  the  actual  splitting  off 
of  particles  of  rock,  the}^  leave  minute  openings  between 
them  into  which  water  may  penetrate  and  begin  its  work  of 
dissolution.    Changes  of  temperature  have  little  effect  upon 


18 


AGRONOMY 


rocks  that  are  not  exposed,  but  the  great  banks  of  irregular 
fragments  at  the  base  of  cliffs  show  how  rapidly  the  work  of 
tearing  down  the  solid  rock  goes  on  under  favorable  condi- 
tions. When  water  is  present  in  the  rocks  the  lowering  of 
the  temperature  below  the  freezing  point  causes  weathering  to 
progress  still  more  rapidly,  since  the  expansive  force  of  water 
in  freezing  is  equal  to  the  weight  of  a  column  of  ice  a  mile 


Photograph  by  E.  Vickers 

Fig.  6.    A  hard  portion  of  a  rocky  ledge 
The  softer  parts  have  been  carried  away  by  the  stream 

high,  or  about  150  tons  to  the  square  foot.  Most  rocks  go  to 
pieces  rapidly  under  alternate  freezing  and  thawing.  Even 
polished  granite  soon  deteriorates  in  severe  climates  through 
the  freezing  of  water  that  finds  its  way  between  the  crystals 
in  the  rock.  The  obelisk  known  as  Cleopatra's  Needle,  which 
resisted  the  atmosphere  of  Egypt  for  many  centuries,  began 
to  deteriorate  at  once  when  removed  to  the  latitude  of  New 
York,  and  had  to  be  protected.  When  pieces  of  the  rock 
have  been  chipped  off  by  the  cold  and  carried  to  the  base 
of    a    cliff    by  gravity,  running  water  may  carry  them  for 


OEIGIN  OF  THE  SOIL  19 

long  distances,  dragging  them  over  the  bed  rock,  grinding 
them  against  other  pieces,  and  rapidly  reducing  them  in  size, 
the  finer  particles  being  carried  away  by  the  current  and 
deposited  elsewhere.  Waterworn  pebbles  are  easily  recog- 
nized by  their  rounded  surfaces,  and  the  fine  sand  and  clay 


Photosraph  l>yTl.  I,.  ITollietcr  Land  Co. 

Fig,  7.   A  mouutaiuuus  regicjii  showing  the  weathered  crests  and 
snow-filled  valleys 

to  be  found  in  every  shallow  are  but  deposits  of  rock  dust 
ground  from  the  pebbles  by  the  streams. 

It  is  not  alone  the  particles  of  rock  in  the  stream  beds 
that  are  carried  away  by  running  water.  During  every  heavy 
rain  the  torrents  of  muddy  water  running  away  from  culti- 
vated fields  show  how  rapidly  the  most  fertile  parts  are  be- 
ing removed.  When  the  current  slackens,  this  material  is 
dropped,  the  largest  particles  first,  the  smallest  much  later. 
The  latter  often  continue  suspended  in  the  water  for  days. 


20  AGRONOMY 

Tlie  delta  at  the  mouth  of  many  large  rivers  is  made  up  of 
these  finer  particles,  and  consequently  delta  soils  are  among 
the  most  fertile  in  the  world. 

Work  of  glaciers.  Another  most  effective  agent  in  grinding 
up  the  bed  rock,  but  one  that  is  no  longer  active  m  our  coun- 
try, was  the  great  ice  sheet  that  ages  ago  spread  from  colder 
regions  southward  over  a  large  part  of  North  America.  One 
or  perhaps  several  of  these  extended  their  movements  to  cen- 
tral Pennsylvania  and  the  Ohio  River  valley,  and  westward 
nearly  to  the  Rocky  Mountains.  In  the  northern  part  of  the 
United  States  the  ice  sheet  was  a  mile  or  more  thick  and 
moved  over  the  country  with  irresistible  force,  breaking  off 
great  fragments  of  rock  as  it  went,  and  now  advancing  with 
a  cold  season,  now  retreating  with  a  warm  one,  ground  the 
immense  rocks  to  bowlders,  the  bowlders  to  pebbles,  the  peb- 
bles to  sand,  and  the  sand  to  powder.  The  interior  of  Green- 
land is  still  covered  with  such  an  ice  sheet,  and  similar 
accumulations  of  ice  in  the  form  of  glaciers  are  found  in 
Switzerland,  the  Rocky  Mountains,  and  other  elevated  parts 
of  the  world,  where  the  process  of  grinding  up  the  bed  rock 
in  this  way  may  still  be  witnessed.  Upon  the  final  retreat  of 
the  ice  sheet  the  country  over  which  it  moved  was  left  strewn 
with  vast  deposits  of  rock  fragments,  and  these,  sometimes 
intermingled,  sometimes  sorted  out  by  running  water  into 
beds  of  clay,  sand,  and  gravel  and  thrown  up  into  hills  and 
ridges,  between  which  were  many  small  lakes  and  marshes, 
cover  much  of  the  country  in  the  northeastern  states.  The 
topography  of  a  glaciated  country  is  quickly  recognized  by 
the  geological  student. 

Modifications  of  the  bed  rock.  It  is  believed  that  not  only 
has  the  mantle  rock  been  derived  from  the  bed  rock  by 
processes  already  noted,  but  that  much  of  the  bed  rock  itself 
was  originally  formed  from  harder  rock  that  was  first  weath- 
ered into  small  particles  and  later  consolidated  by  various 


ORIGIN  OF  THE  SOIL  21 

forces.  The  rocks  from  wliicli  all  the  other  rocks  are  sup- 
posed to  have  been  derived  are  called  igneous  rocks.  They 
are  hard  and  compact,  and  include  the  granites,  diorites,  ba- 
salts, and  lavas.  Usually  they  are  found  deep  in  the  earth 
and  are  buried  under  not  only  many  feet  of  mantle  rock  but 
of  other  bed  rocks  as  well.    Rocks  derived  from  the  igneous 


Photosraph  liy  II.  L.  Ilollisfer  Land  Co. 

Fig.  8.    Glacier-covered  slope  in  the  Rocky  Mountains 
Note  the  banks  of  rock  fragments  which  have  been  carried  down  by  the  ice 

rocks  are  called  sedimentary,  or  aqueous,  rocks  because  they  are 
regarded  as  having  first  been  laid  down  in  the  bottom  of  shal- 
low lakes  or  seas  as  beds  of  mud,  sand,  or  gravel,  and  later 
compacted  into  rock.  Limestones,  sandstones,  and  shales  are 
some  of  the  better-known  sedimentary  rocks.  Some  of  the 
sedimentary  rocks  have  been  subjected  to  great  heat  and 
pressure  since  their  formation,  thus  altering  their  structure. 
Such  rocks    are  called   metamorphie  rocks.    Slates,  marbles, 


22  AGRONOMY 

and  quartzites  are  good  illustrations  of  metamorphic  rocks. 
By  consulting  the  following  table  the  student  should  have 
no  difficulty  in  discovering  to  which  group  the  rocks  in 
his  own  region  belong. 

TABLE  OF  ROCKS 
I.  Igneous. 

1.  Granite. 

2.  Basalt. 

3.  Diorite. 

4.  Lava. 

IL  Sedimextary,  or  Aqueous. 

A.  Inorganic. 

1.  Argillaceous  —  shale  (formed  from  clay). 

2.  Silicious. 

a.  Sandstone  (formed  from  sand). 

b.  Conglomerate  (formed  from  pebbles). 

c.  Breccias  (formed  from  irregular  fragments). 

3.  Chemical  — bog  iron,  rock  salt,  gypsum. 

B.  Organic. 

1.  Calcareous  —  limestone  (formed  from  animal  remains). 

2.  Carbonaceous  —  soft  coals  (formed  from  2)lant8). 

3.  Silicious  —  diatom  earth,  chert. 

III.  Metamorphic. 

1.  Slate  (derived  from  shale). 

2.  Quartzite  (derived  from  sandstone). 

3.  Marble  (derived  from  limestone). 

4.  Anthracite  (derived  from  soft  coals). 

Changes  in  mantle  rock.  The  weathered  fragments  of  the 
bed  rock  have  not  lain  undisturbed  where  they  fell.  The 
work  of  weathering  is  unceasing.  Little  by  little  the  parti- 
cles have  been  reduced  in  size ;  running  water  has  sorted 
them  over  time  and  again ;  floods  from  the  melting  ice  sheet 
have  spread  them  out ;  ants,  earthworms,  and  other  animals 
have  slowly  turned  them  over,  bringing  deeper  layers  to  the 


ORIGIN  OF  THE  SOIL  23 

surface;  generation  after  generation  of  plants  have  grown 
in  the  debris,  and,  dying,  have  left  theii'  remains  to  enrich 
the  deposit ;  bacteria,  the  smallest  of  living  things,  have 
here  found  a  congenial  home  and  have  added  their  share  to 


Fig.  9.   A  glaciated  valley  in  southern  New  York 
Note  the  irregular  surface 

the  cycle  of  changes ;  thus  have  the  ragged  fragments  of  rock 
that  in  the  beginning  were  unable  to  support  the  growth  of 
plants  been  turned  into  the  rich  and  fertile  soil  in  which 
are  grown  the  luxuriant  crops  upon  which  the  very  life  of 
man  depends. 


24  AGRONOMY 

PRACTICAL   EXERCISES 

1.  In  the  school  garden  measure  the  depth  of  the  soil  by  making  an 
opening  down  to  the  subsoil.  Compare  this  as  to  depth  with  any  other 
soil  sections  with  which  you  are  familiar. 

2.  Ascertain  from  wells,  railway  cuts,  trenches  for  sewers,  and  the 
like  the  average  depth  of  the  mantle  rock  in  your  vicinity. 

3.  If  the  mantle  rock  varies  in  depth  in  your  locality,  make  a  table 
to  show  this. 

4.  Make  a  collection  of  sj^ecimens  to  illustrate  the  kinds  of  rock  in 
the  table  on  page  22. 

5.  Make  a  list  of  the  different  kinds  of  bed  rock  in  your  vicinity. 

6.  Visit  a  gravel  pit  and  collect  as  many  different  kinds  of  rock 
fragments  as  possible. 

7.  Make  a  list  of  all  the  above-mentioned  fragments  that  are  unlike 
the  bed  rock  in  your  region. 

8.  Visit  the  best  farm  or  garden  in  the  vicinity  and  decide  whether 
the  soil  is  a  sedentary  or  a  transported  one. 

9.  Visit  the  nearest  outcrop  of  rock  and  search  for  signs  of  weath- 
ering. Make  a  list  of  all  forms  seen.  Decide  which  is  more  effective 
in  that  place. 

10.  Make  a  similar  visit  to  a  field  on  a  hillside. 

11.  Account  for  differences  in  the  color  of  the  soil  on  hilltops  and 
in  lowlands.    In  which  are  the  crops  best ?   Why? 

References 

Dryer,  "Lessons  in  Physical  Geography." 
Gilbert  and  Brigham,  "  Physical  Geography." 
King,  "The  Soil." 
Salisbury,  "  Physiography." 


CHAPTER  III 

TYPES  OF  SOILS 

Named  for  their  origin.  Soils,  as  we  have  seen,  may  be 
divided  into  residual  and  drift  soils,  depending  upon  whether 
they  have  originated  from  the  underlying  rocks  or  have  been 
transported  from  distant  regions  by  water  and  other  agencies. 


^Nii2Bi9^3HEHHBHB8HiHIHtB8BB 

■"^ 

^^^^^^^^^HC^' 

-•"1 

■^^P"w- 

f" 

'  '-^  S '''  ^k^^^'^l^^^M 

Fig.  10.   Vegetation  invading  a  shallow  lake 

It  is  possible,  also,  to  name  the  soils  from  the  agencies  most 
active  in  forming  them,  and  the  principal  groups  thus  natu- 
rally break  up  into  smaller  divisions.  The  residual  soils  may  be 
divided  into  the  true  sedimentary  and  the  lacustrine,  while  drift 
soils  include  the  aeolian,  volcanic,  colluvial,  glacial,  arid  alluvial. 

25 


26 


AGRONOMY 


Photograph  from  Aiiiencau  stetl  and  Wire  Co. 

Fig.  11.   A  small  pond  nearly  filled  with  aquatic  vegetation 


Sedentary  soils.  Sedentary  soils  are  formed  from  the  under- 
lying rock,  either  by  decomposition,  disintegration,  or  by  a 
combination  of  both.  In  limestone  regions  the  soluble  part 
of  the  rock  may  be  carried  a\\  ay  by  the  water,  leaving  a  soil 


TYPES  OF  SOILS 


27 


quite  unlike  one  made  from  limestone  fragments.  Such  soils 
may  actually  need  to  have  lime  added  to  them  to  enable  them 
to  produce  good  crops.  Sandstone  rocks  are  formed  of  grains 
of  sand  cemented  together  by  lime,  clay,  iron,  or  silica.  When 
the  cementing  material  is  dissolved  out  by  water,  a  sandy  soil 
is  left.  Other  residual  soils  may  be  formed  from  weathered 
fragments  of  the  origmal  rock  from  which  little  has  been  car- 
ried away  by  water,  as  in  many  soils  derived  from  granite  rocks. 


Fig.  12.    A  movina;  saiul  dune 


Pliotograph  by  A.  li  Klugh 


Lacustrine  soils.  These  differ  from  true  residual  soils  in 
having  been  built  up  in  lakes  and  ponds  by  an  accumulation  of 
plant  and  animal  remains,  together  with  fine  particles  of  rock 
brought  in  by  rams  or  blown  in  by  wind.  In  our  Northern  states 
many  of  what  were  once  shallow  lakes  have  been  completely 
filled  in  this  way  and  now  contain  a  rich  black  soil  much  valued 
for  growing  certain  crops,  such  as  celery.  Such  soils,  however, 
often  lack  some  of  the  minerals  needed  by  plants,  and  these 
have  to  be  supplied  before  good  crops  can  be  produced. 


28 


AGKONOMY 


^olian  soils.  These  have  been  transported  by  wind.  Sand 
dunes  are  famiUar  examples.  Less  well  known,  though  more 
important,  are  the  deposits  of  wind-blown  materials  known  as 
loess  that  cover  large  areas  in  China,  Europe,  and  parts  of  the 
Middle  West.  Loess  is  composed  of  particles  much  finer  than 
sand  grains  and  makes  very  fertile  soils.  Parts  of  Iowa  and 
Kansas  are  covered  with  loess  to  the  depth  of  hundreds  of  feet. 


Plioto-rapli  by  A.  B.  Kliigh 

Fig.  13.   A  sand  dune  captured  by  vegetation 


Volcanic  soils.  As  the  name  indicates,  these  are  formed  of 
the  ashes  and  dust  thrown  out  by  volcanoes.  They  are  rare 
in  the  United  States  except  in  the  Far  West,  but  in  other 
countries  are  often  encountered.  After  weathering,  they  form 
very  fertile  soils.  Much  of  the  land  cultivated  in  the  Hawaiian 
Islands  is  of  this  type. 

CoUuvial  soils.  These  have  been  formed  by  gravity  acting 
upon  the  pieces  of  rock  quarried  from  the  cliffs  by  changes  of 
temperature  and  freezing  water.    Good  illustrations  are  found 


TYPES  OF  SOILS 


29 


in  the  banks  of  talus  at  the  base  of  cliffs  almost  anywhere. 
The  soil  brought  down  by  avalanches  also  belongs  to  this 
class.  Since  the  materials  that  compose  it  are  coarse,  rough, 
and  irregular,  a  colluvial  soil  is  of  little  value  for  cultivation, 
though  it  may  support  a  luxuriant  growth  of  lichens,  mosses, 
ferns,  and  small  shrubs.  The  soil  on  hillsides  may  also  be 
regarded  as  partly  colluvial. 

Glacial  soils.  Glacial  soils  have  been  derived  from  many 
kinds  of  bed  rock  by  the  glacial  ice  that  once  covered  a  great 
part  of  the  northeast- 
ern states  and  various 
other  parts  of  the  earth. 
They  consist  of  sand, 
clay,  and  gravels  either 
separate  or  intermin- 
gled. Such  soils  are 
the  rule  in  the  states 
north  of  the  Ohio  River 
and  east  of  the  Great 
Plains,  but  south  and 
west  they  gradually 
thin  out  and  disappear. 

Alluvial  soils.  These 
have  been  transported 
by  streams  that  during 
periods  of  flood  pick  up  much  material  that  is  dropped  as  soon 
as  the  current  slackens.  The  soil  in  our  ordinary  bottom  lands 
has  been  formed  in  this  way,  and  the  soil  in  the  delta  region 
along  the  lower  Mississippi  is  of  the  same  nature.  Alluvial 
soils  are  extremely  fertile,  since  they  consist  in  great  measure 
of  the  richest  soil  washed  down  from  other  fields. 

Soil  constituents.  Ordinary  arable  land  is  a  mixture  of 
various  ingredients.  When  these  are  separated,  we  know 
them  as  sand,  clay,  silt,  humus,  and  the  like.    Peat  is  a  black 


Fig.  14.    A  ridge  of  glacial  debris  that  has 
been  sorted  by  running  water 


30 


AGRONOMY 


deposit  formed  by  the  decay  of  plants  under  water,  and  may 
be  seen  in  the  process  of  formation  along  the  shores  of  many 
lakes  and  ponds.  It  also  occurs  in  extensive  deposits  called 
peat  bogs,  which  mark  the  site  of  old  lakes  that  have  been 
filled  by  such  accumulations.  When  pure,  peat  contains 
enough  carbon  to  make  it  useful  as  fuel.    Most  of  our  coal 

beds  have  been 
formed  from  peat. 
Humus,  sometimes 
called  vegetable 
mold  or  leaf  mold, 
is,  like  peat,  formed 
from  plant  remains, 
but  in  this  case  the 
decay  has  taken 
place  in  or  on  tlie 
soil.  It  is  a  black, 
loose  substance 
usually  abundant 
on  the  forest  floor 
and  is  an  indispen- 
sable element  in  all 
fertile  soils.  Muck 
is  a  black  deposit, 
midway  between 
humus  and  peat,  that  occurs  in  swamps  and  low  grounds.  The 
words  "  peat "  and  "  muck  "  are  often  used  rather  loosely  to 
designate  the  same  substance.  Marl  is  a  deposit  of  lime  and 
clay,  like  a  whitish  mud,  which  forms  at  the  bottom  of  ponds. 
The  lime  is  derived  from  the  decay  of  the  shells  and  bones 
of  water  animals.  Marl  is  valued  for  adding  to  soils  deficient 
in  lime.  Clay  is  a  soft  powder  or  rock  flour  usually  resulting 
from  the  weathering  of  feldspar  rocks.  Clay  consists  of  parti- 
cles less  than  one  five  thousandth  of  a  millimeter  in  diameter, 


Fig.  15. 


Section  of  an  abandoned  quarry  partly 
filled  with  water 


The  dark  deposit  at  the  top  of  the  exposure  is  peat, 

tlie  light  material  below  is  marl,  beneath  this  is  the 

mautle  rock  which  merges  into  the  bed  rock 


TYPES  OF  SOILS  31 

and  a  cubic  foot  of  it  weighs  from  seventy-five  to  eiglity 
pounds.  Cla}^  is  powdery  when  dry,  sticky  when  wet,  and  is 
easily  molded.  Silt  consists  of  particles  somewhat  coarser  than 
clay.  They  range  in  diameter  from  five  thousandths  to  five 
hundredths  of  a  millimeter.  When  moist,  silt  becomes  a  soft 
mud,  and  in  drymg  inclines  to  crumble.  Sand  consists  of  loose 
hard  grains  from  five  hundredths  of  a  millimeter  to  one  milli- 
meter in  diameter,  resulting  from  the  weathering  of  sandstones 
and  quartzes.  The  grains  may  be  angular  or  rounded,  but  are 
always  harsh  and  granular  to  the  touch.  A  cubic  foot  of  sand 
weighs  from  one  hundred  to  one  hundred  ten  pounds.  Wet 
sand  is  held  together  by  the  moisture ;  when  dry,  the  grains 
at  once  fall  apart.  Crravel  is  a  mixture  of  many  kinds  of  rock 
fragments  and  differs  from  sand  chiefly  in  the  size  of  the  parti- 
cles composing  it.  The  smaller  fragments  are  called  pebbles ; 
the  larger,  bowlders.  Glacial  pebbles  are  angular  in  shape. 
When  pebbles  are  rounded  it  is  an  indication  that  they  have 
been  worked  over  by  water.  Gravel  is  usually  accompanied 
by  varying  amounts  of  sand  and  clay,  and  often  forms  rich 
soils.  Peat,  muck,  marl,  and  humus  are  all  of  organic  origin ; 
clay,  silt,  sand,  and  gravel  are  inorganic.  The  nature  of  the 
soil  greatly  influences  the  plants  that  grow  on  it.  This  is  shown 
from  the  fact  that  plants  on  the  same  kind  of  soil  in  different 
parts  of  the  world  resemble  one  another. 

Sand  and  clay  contrasted.  The  best  soil  for  ordinary  crops 
is  a  mixture  of  clay,  sand,  silt,  and  humus.  Owing  to  the 
contrasting  characters  of  clay  and  sand,  the  soil  is  heavy  or 
light,  cold  or  warm,  moist  or  dry,  worked  with  difficulty  or 
easily  worked,  according  to  whether  one  or  the  other  predom- 
inates. Neither  forms  a  good  soil  by  itself,  but  intermingled 
in  various  proportions  they  give  a  wide  range  of  soils  from 
which  the  farmer  and  gardener  can  select  one  suited  to  the 
crop  he  proposes  to  grow.  Clay  consists  of  the  finest  of  soil 
particles.    It  would  require  400,000  of  the  smallest,  side  by 


32 


TYPES  OF  SOILS  33 

side,  to  measure  an  inch.  Clay  is  slow  to  absorb  water,  and  its 
reluctance  in  this  -  respect  causes  it  to  gully  badly  in  heavy 
storms.  It  is  equally  slow  to  give  up  moisture  once  absorbed. 
The  particles  of  wet  clay  cling  together  with  great  tenacity, 
and  as  they  dry  they  form  a  compact  mass  traversed  by 
numerous  cracks,  due  to  the  shrinking  of  the  mass  as  the 
water  evaporates.  The  total  surface  of  the  particles  of  clay 
to  which  the  water  clings  is  very  great.  When  thoroughly  wet 
it  is  able  to  hold  much  water,  often  as  much  as  40  per  cent. 
In  wet  weather,  therefore,  it  may  contain  too  much  water  for 
good  crops,  while  in  dry  weather  it  may  bake  and  become  too 
hard  for  the  roots  of  plants  to  penetrate.  Owing  to  its  great 
water  content,  it  warms  slowly,  but  it  cools  as  slowly,  and  in 
autumn  the  vegetation  lasts  longest  on  the  clays.  Because  of 
the  smallness  of  the  particles  composing  clay,  the  air  spaces  are 
correspondingly  small.  In  consequence  the  air  cannot  move 
through  it  freely  and  it  is  always  poorly  aerated  in  spite  of 
the  fact  that  it  contains  a  greater  amount  of  pore  space  than 
sand.  Clay  is  the  source  of  considerable  plant  food,  mostly 
potash,  and  it  also  fixes  other  plant  foods  that  may  be  in  the 
soil.  The  farmer  calls  clay  a  cold  and  heavy  soil,  but  the 
heaviness  refers  to  the  difficulty  with  which  it  is  worked,  and 
not  to  its  weight,  for  it  is  much  lighter  than  sand. 

Sand  consists  of  hard  separate  grains.  These  have  little 
tendency  to  stick  together,  even  when  wet,  though  in  certain 
positions,  as  on  seabeaches,  they  may  form  a  firm,  hard  sur- 
face when  saturated  with  water.  Sand  does  not  bake  nor 
crack,  and  in  drying  returns  to  the  loosely  granular  form.  It 
absorbs  water  readily  and  as  readily  gives  it  up.  It  often  con- 
tains less  than  5  per  cent  of  water.  Plants,  however,  can  get 
more  of  the  contained  moisture  from  sand  than  from  clay. 
Sand  does  not  gully  as  badly  as  clay  because  it  so  rapidly 
absorbs  water.  It  warms  up  quickly  and  cools  much  more 
rapidly  than  clay.    Owing  to  its  large  air  spaces,  air  moves 


34  AGKONOMY 

through  it  readily.  Sand  contains  very  little  plant  food  be- 
cause this  is  so  easily  washed  out  by  the  rains.  It  is  called  a 
light  soil  because  it  is  so  easily  worked,  though,  bulk  for 
bulk,  it  is  heavier  than  any  other.  The  roots  of  plants  pene- 
trate sand  without  difficulty,  but  the  readiness  with  which  it 
parts  with  its  moisture  renders  it  unsuitable  for  most  crops. 
Like  clay,  sand  is  of  a  variety  of  colors.  Keds  and  yellows,  due 
to  compounds  of  iron,  are  most  abundant. 

Loam.  A  soil  containing  about  equal  parts  of  sand  and 
clay  with  some  humus  is  called  loam.  If  the  sand  is  in  excess, 
it  is  called  a  sandy  loam ;  if  the  clay  predominates,  it  is  a 
clay  loam.  Other  constituents  in  the  soil  may  modify  it  suf- 
ficiently to  entitle  it  to  some  other  designation,  as  silt  loam  or 
gravelly  loam.  Clay  soils  have  from  80  to  100  per  cent  of  clay  ; 
clay  loams,  from  60  to  80  per  cent.  Sandy  soils  have  from 
80  to  100  per  cent  of  sand ;  sandy  loams,  from  60  to  80  per 
cent.  The  national  Department  of  Agriculture  is  at  present 
analyzing  and  mapping  the  soils  of  the  United  States.  As 
fast  as  mapped,  each  type  of  soil  is  given  a  name  to  distin- 
guish it.  This  is  usually  derived  from  some  town  located 
upon  the  soil  indicated,  as  Hammond  silt  loam,  llagerstown 
loam,  and  Miami  sand. 

Alkali  soils.  In  various  parts  of  the  West  the  soils  contain 
an  excess  of  the  salts  of  sodium,  magnesium,  calcium,  and  potas- 
sium, in  which  the  ordinary  cultivated  plants  will  not  grow. 
Such  soils  are  known  as  alkali  soils.  They  usually  occur 
in  regions  deficient  in  rainfall,  and  the  deposits  are  due  to  the 
fact  that  the  water  from  the  scanty  rains  soon  evaporates,  leav- 
ing on  the  surface  the  salts  it  has  dissolved  out  of  the  soil. 
Among  these  salts  may  be  such  familiar  substances  as  common 
table  salt,  Glauber  and  Epsom  salts,  and  sal  soda.  Many 
wild  plants  are  not  very  sensitive  to  these  salts  and  may 
even  tlu-ive  in  such  soils,  but  before  the  crops  of  the  farmer 
will  grow,  the  alkali  must  be  removed.   In  many  soils  this  is 


TYPES  OF  SOILS 


35 


I 


accomplished  by  flooding  with  water.  In  ushig  this  means  care 
must  be  taken  to  see  that  proper  underdrainage  is  provided 
by  means  of  tiles,  if  the  natural  drainage  is  not  sufficient. 

Acid  soils.  Some  soils  will  not  support  a  good  growth  of 
cultivated  crops  because  of  various  acids  left  in  them  by  the 
decaying  vegetation,  which  hmder  the  growth  of  the  bacteria 
necessary  to  turn  the  humus  into  available  plant  food.  Such 
soils  are  called  acid,  or  sour,  soils.  Though  not  adapted  to  ordi- 
nary crops,  sour  soils  may  support  a  luxuriant  vegetation,  and 
some  wild  plants  have  become  so  accustomed  to  acid  soils  that 
they  will  thrive  in  no 
other.  Among  plants 
of  this  kind  may  be 
mentioned  huckleber- 
ries, cranberries,  trail- 
ing arbutus,  and  many 
other  plants  of  the  heath 
family.  Most  of  the 
plants  found  in  peat 
bogs  are  lovers  of  acid 
soils.  On  the  other 
hand,  clover,  beans, 
peas,  and  other  legumes  are  very  intolerant  of  such  soils  and 
cannot  live  in  them.  Lettuce,  beets,  spinach,  and  timothy  are 
other  plants  that  will  not  grow  in  sour  soils.  The  majority  of 
sour  soils  are  found  in  low  and  poorly  drained  districts,  but 
the  proper  combination  of  conditions  will  turn  any  soil  acid, 
and  many  upland  soils  are  of  this  kind.  The  bird's-foot  violet, 
sorrel,  and  beard  grass  (^Andropo(/on^  are  regarded  as  indica- 
tors of  acid  soils  in  uplands.  When  mosses  grow  on  the  lawn 
or  in  the  fields  it  is  also  a  pretty  sure  hidication  of  a  sour  soil. 

A  test  for  acid  soils.  To  discover  whether  a  given  soil  is 
acid  or  not,  make  it  into  a  thin  mortar  with  water  and  test 
with  blue  litmus  paper,  or  inclose  a  piece  of  the  paper  in  a  ball 


Fkj.  17.  a  pitcher  plant  (Sarraceniu),  a  char- 
acteristic plant  of  acid  soils 


36  AGRONOMY 

of  the  moist  soil  for  a  few  minutes.  If  the  paper  turns  red,  the 
soil  is  acid.  Litmus  paper  may  be  found  in  any  chemical 
laboratory  or  at  the  nearest  drug  store.  Blue  litmus  paper  has 
the  property  of  turning  red  in  the  presence  of  acids,  and  red 
litmus  paper  will  turn  blue  in  alkaline  mediums.  Acid  soils  are 
easily  neutralized  by  the  application  of  lime,  marl,  or  gypsum. 
Artificial  soils.  The  florist  and  gardener  often  find  it  expe- 
dient to  make  artificial  soils  for  their  plants.  Seedings  and  cut- 
tings need  a  light  and  porous  soil  consisting  largely  of  sand ; 
ferns  need  a  considerable  proportion  of  humus.  The  grower, 
therefore,  usually  obtains  peat,  sand,  leaf  mold,  and  other  in- 
gredients and  mixes  his  soil  to  suit  the  needs  of  the  plants.  A 
good  potting  soil  for  all  ordinary  plants  is  made  by  building  up 
a  mound  consisting  of  a  layer  of  sods  from  any  good  soil,  a  layer 
of  sand,  and  a  layer  of  stable  manure ;  then  another  layer  of  sods, 
sand,  and  manure,  and  so  on.  This  is  allowed  to  stand  until 
the  sods  have  decayed,  after  which  it  is  thoroughly  mixed  and 
is  ready  for  use. 

PRACTICAL  EXERCISES 

1.  On  a  soil  map  of  your  region  locate  such  types  of  sedimentary 
and  drift  soils  as  occur. 

2.  What  is  the  name  of  the  soil  upon  which  the  school  garden  is 
located  ?   your  own  home  ? 

3.  Visit  deposits  of  sand,  clay,  peat,  marl,  and  humus  and  collect 
good  samples  of  each  for  study. 

4.  Weigh  a  cubic  foot  of  soil  from  the  school  garden  and  estimate 
the  number  .of  tons  in  an  acre  7  in.  deep. 

5.  Test  the  soil  in  the  school  garden  and  in  your  own  garden  for 
acidity.    Make  the  same  test  of  the  soil  in  the  nearest  peat  bog. 

6.  Make  a  list  of  the  more  conspicuous  plants  in  a  peat  bog.  Com- 
pare with  a  similar  list  from  a  meadow  or  pasture. 

7.  Pour  ammonia  water  through  a  tube  filled  with  powdered  clay  and 
examine  that  which  filters  through.   What  has  become  of  the  ammonia  ? 

8.  Measure  out  equal  amounts  of  sand  and  clay  and  place  in  sepa- 
rate vessels.  Add  measured  quantities  of  water  to  each  until  they  are 
saturated.    Which  absorbs  water  more  rapidly?    Which  absorbs  the 


I 


TYPES  OF  SOILS 


37 


greater  amount  ?    What  per  cent  of  water  did  each  absorb  ?     What 
filled  the  space  before  the  water  entered  ? 

9.  Fill  a  two-quart  jar  about  two  thirds  full  of  soil  from  the  school 
garden.  Add  water  until  the  jar  is  full  and  let  stand  for  a  day.  Then 
shake  thoroughly  and  let  the  mixture  settle.  How  do  the  various  mate- 
rials arrange  themselves  in  settling?  Determine  from  the  experiment 
the  kind  of  loam  your  soil  is  most  like.  Try  the  same  experiment  with 
the  subsoil.    Is  the  result  the  same  ? 

10.  Put  about  a  pint  each  of  soil  and  subsoil  from  the  school  garden 
into  air-tight  receptacles  and  bring  into  the  laboratory.  Test  for  mois- 
ture and  organic  content  as  follows  :  Procure  two  small  pans  and  weigh 
them.  Place  100  g.  of  soil  in  one  and  a  like  amount  of  subsoil  in  the 
other,  weighing  quickly  to  avoid  loss  by  evaporation.  Expose  the  soil 
to  the  air  of  the  room  for  three  days  and  weigh  pan  and  soil  again. 
The  difference  between  this  and  the  former  weight  will  give  the  amount 
of  capillary  water  each  specimen  contained.  Now  get  two  crucibles  and 
place  10  or  15  g.  of  the  dry  soil  and  subsoil  in  them.  Heat  in  an  oven 
for  five  hours  and  weigh  again.  The  difference  in  weight  gives  the 
amount  of  the  hygroscopic  moisture  present.  Next  heat  each  sample 
to  red  heat  over  a  Bunsen  burner  for  half  an  hour  and  weigh  again. 
The  difference  now  represents  roughly  the  amount  of  organic  material 
in  the  soil.    Fill  out  the  following  table  : 


Subsoil 


AVeight  of  soil  pan 

Weight  of  pan  and  moist  soil .... 
Weight  of  pan  and  air-dry  soil  .  .  . 
Amount  of  capillary  moisture       .     .     . 

Weight  of  crucible 

Weight  of  crucible  and  soil  after  baking 
Amount  of  hygroscopic  water  found 
Weight  of  crucible  after  burning      .     . 
Amount  of  organic  matter  present    . 


11.  Breathe  upon  a  glass  slide,  throw  some  sand  upon  it,  shake  off  all 
loose  grains,  and  examine  those  that  remain  with  the  microscope.  The 
pink  or  black  particles  are  hornblende ;  the  thin,  clear,  or  dusky  flakes 
are  mica  ;  and  the  gray  particles  are  feldspar  or  granite.  Mix  up  some  clay 
in  water  and  examine  a  drop  of  the  turbid  fluid  in  the  same  way.  How 
do  the  two  mounts  compare  as  to  size  and  composition  of  the  particles  ? 


442842 


CHAPTER  IV 

CONDITIONS  AFFECTING  SOIL  FERTILITY 

Structure.  While  humus,  water,  and  air  are  necessary 
constituents,  mineral  matter  is  the  basis  of  all  fertile  soils, 
formmg  from  60  to  90  per  cent  of  their  weight.  The  prevail- 
ing mineral  constituent  is  nearly  always  silica,  with  varying 
amounts  of  alumina  or  clay  and  the  oxides  of  iron,  calcium, 
magnesium,  and  others.  Even  in  the  poorest  soils  there  are 
enough  of  the  elements  needed  by  plants  for  at  least  a  hundred 
ordinary  crops,  and  the  subsoil  contains  immense  additional  sup- 
plies ;  but  these  are  often  so  solidly  bound  in  the  rocks  as  to  be 
only  slowly  available  to  plants.  The  texture  of  the  soil,  then, 
determines  in  great  measure  not  only  what  crops  can  grow 
upon  it,  but  the  rapidity  with  which  weathering  can  make  the 
needed  elements  available.  A  block  of  stone  will  support  only 
a  few  mosses  and  lichens ;  grind  it  to  sand  and  many  more 
highly  specialized  plants  will  grow  upon  it ;  reduce  it  to  pow- 
der and  it  will  grow  our  cultivated  crops.  A  gram  of  good 
soil  contains  from  two  billions  to  twenty  billions  of  soil  par- 
ticles. In  a  cubic  foot  of  the  finest  clay  the  total  exposed 
surface  of  the  particles  is  not  far  from  175,000  square  feet.  In 
a  sandy  soil  the  area  falls  to  about  10,000  square  feet.  The 
particles  in  a  cubic  foot  of  light  loam  have  a  total  surface  area 
of  about  one  acre.  Since  water  containing  the  dissolved  food 
materials  is  held  on  the  surface  of  these  particles,  one  easily 
understands  how  a  fine  soil  and  a  fertile  soil  are  nearly 
synonymous  terms.  In  the  soil  the  finest  particles  are  not 
separate,  but  are  Jloceulated,  or  bound  together  in  small  groups 
called  soil  cnanbs.    When  for  any  reason  the  soil  crumbs  are 

38 


CONDITIONS  AFFECTING  SOIL  FERTILITY       39 

broken  down  into  their  original  particles,  the  soil  is  said  to 
be  puddled.  The  roots  of  plants,  and  the  water  and  air  nec- 
essary for  their  growth,  have  difficulty  in  penetrating  pud- 
dled soils,  and  the  farmer  is  careful  not  to  work  his  land 
when  doing  so  may  induce  this  condition.  Puddled  clay  is 
so  impervious  to  water  that  it  is  often  placed  in  the  bottom 
of  artificial  ponds  to  prevent  the  water  from  leaking  out. 


Fig.  18.    A  stony  field  in  southern  New  York,  showing  glacial  debris 
At  the  time  the  photograph  was  taken  this  field  was  planted  with  corn 

The  presence  of  lime  and  humus  also  has  considerable 
effect  on  the  texture  of  the  soil.  Lime  has  the  faculty  of 
flocculating  clay  soils,  but  in  sandy  soils  small  amounts 
of  lime  serve  to  bind  the  particles  together;  in  addition,  it 
serves  to  correct  acid  soils  and  promotes  the  growth  of  the 
soil  bacteria.  Humus  makes  heavy  soils  more  open  and  pro- 
motes the  movement  of  air  in  them,  thus  making  them 
warmer.    It  also  absorbs   and   holds   for   the   plants   nearly 


40  AGRONOMY 

twice  its  weight  of  water  and  is  the  source  of  most  of  the 
nitrogen  used  by  them. 

The  air.  We  are  living  at  the  bottom  of  an  ocean  of  air 
from  which  all  the  animals  and  plants  derive  elements  neces- 
sary to  existence.  From  it  animals  obtain  the  oxygen  for  res- 
piration, while  the  plants,  in  addition  to  a  similar  use  of  oxygen, 
make  use  of  the  carbon  dioxide,  forming  from  it  nearly  half 
their  dry  weight.  The  air  is  made  up  of  several  gases,  two 
of  wliich,  oxygen  and  nitrogen,  comprise  more  than  98  per  cent 
of  its  bulk.  The  proportions  of  the  principal  gases  are  given 
in  the  following  table : 

Nitrogen 77.95 

Oxygen 20.61 

Water  vajwr  (average)        1.40 

Argon 1.00 

Carbon  dioxide 0.03 

The  air  also  contains  small  quantities  of  krypton  and  neon. 
Water  vapor,  which  varies  in  quantity  with  the  locality,  is 
not  strictly  a  part  of  the  air.  The  air  is  possibly  several  hun- 
dred miles  deep  and  at  sea  level  presses  on  every  square  inch 
of  surface  with  a  weight  of  nearly  15  pounds,  or  more  than 
46,000  tons,  to  the  acre.  The  pressure  varies  somewhat  with 
the  weather,  being  greatest  in  calm,  fine  weather  and  least  as 
a  storm  approaches.  Differences  in  pressure  are  measured  by 
the  barometer,  in  which  a  column  of  mercury  rises  with  high 
pressure  and  lowers  with  a  decrease  of  pressure.  These  varia- 
tions in  pressure  exert  a  considerable  influence  over  the  air 
and  water  in  the  soil.  When  the  barometer  is  falling,  the  les- 
sened pressure  causes  the  air  to  flow  out  of  caves,  mines,  and 
other  underground  cavities,  while  the  water  in  wells  rises  and 
springs  flow  more  copiously.  In  some  localities  the  underly- 
ing porous  rocks  absorb  so  much  air  when  the  pressure  is  high 
that  when  it  is  relaxed  the  amount  of  air  rising  from  wells 
and  other  openings  in  the  soil  may  be  sufficient  to  cause  a 


CONDITIONS  AFFECTING  SOIL  FERTILITY       41 

perceptible  draft.  Wells  of  this  kind  are  called  blowing  wells 
and  form  very  good  natural  barometers.  When  a  storm  ap- 
proaches, the  draft  is  outward,  and  when  fair  weather  returns, 
the  air  flows  back  into  the  ground.  The  same  phenomena  aid 
in  the  ventilation  of  the  soil,  but  even  without  this  there  is 
more  or  less  exchange  between  the  gases  in  the  soil  and  those 
outside  by  a  process  of  diffusion,  in  which  different  gases  tend 
to  mix  until  all  parts  of  the  mixture  have  equal  amounts  of 
each.  The  ventilation  of  the  soil  is  also  promoted  by  the  air 
which  flows  in  when  the  water,  after  a  rain,  sinks  downward. 

Air  in  the  solL  About  half  the  bulk  of  dry  soil  is  pore 
space  filled  with  air.  Clay,  although  apparently  more  com- 
pact than  sand,  has  a  greater  amount  of  pore  space.  The 
spaces,  however,  are  smaller  and  the  air  moves  more  freely 
in  sand.  As  has  been  previously  stated,  air  is  essential  to  a 
fertile  soil.  It  supplies  the  underground  parts  of  plants  with 
the  oxygen  necessary  for  respiration,  it  makes  the  soil  warmer, 
promotes  the  growth  of  soil  bacteria,  and  aids  in  weathering. 
Ordinary  plants  cannot  live  in  a  saturated  soil,  and  a  few  days' 
flooding  may  destroy  an  entire  crop.  Certain  aquatic  plants 
thrive  in  such  soils,  but  these  have  become  adapted  to  their 
habitat  and  have  other  ways  of  obtaining  their  oxygen. 

Temperature.  All  parts  of  the  earth  receive  the  same  amount 
of  sunlight  in  the  course  of  a  year,  but  the  shape  of  our  planet 
makes  the  distribution  of  temperature  very  uneven.  The  heat 
is  greatest  where  the  sun's  rays  are  vertical  and  least  where 
they  fall  obliquely,  since  in  the  latter  case  the  same  amount  of 
heat  is  distributed  over  a  greater  area.  For  this  reason  hill- 
sides sloping  toward  the  sun  are  warmer  than  level  fields, 
while  northern  slopes  are  colder.  Few  realize  the  enormous 
heat  received  from  the  sun,  although  familiar  with  the  fact 
that  a  lens  may  bring  together  the  few  rays  that  fall  upon  it 
and  set  fire  to  paper  or  wood.  It  is  estimated  that  the  energy 
received  from  the  sun  is  equal  to  one  horse  power  per  hour  for 


42 


AGRONOMY 


every  square  yard  of  surface.  A  man  of  average  size  lying  on 
the  earth  will  receive  more  heat  in  one  hour  than  is  needed  to 
raise  a  gallon  of  wat^r  to  the  boiling  point.  The  same  heat 
would  raise  the  temperature  of  a  layer  of  soil,  lialf  an  inch 
thick,  nearly  90  degrees. 

Variations  in  temperature.  Tlie  changes  of  the  seasons  and 
the  alternations  of  day  and  night  cause  the  temperature  of 
middle  latitudes  to  range  from  many  degrees  below  zero  to 
more  than  a  hundred  above  in  the  course  of  a  year.  These 
changes  affect  the  soil  for  some  distance  downward,  though 

in  most  parts  of  the  United 
States  the  difference  between 
the  day  and  night  tempera- 
tures is  not  perceptible  three 
feet  below  the  surface,  and  at 
seventy-five  feet  below,  sum- 
mer's heat  and  winter's  cold 
are  alike  unknown.  This  ex- 
plains the  fact  that  water 
from  deep  wells  is  cool  even 
in  summer.  In  the  tropics 
this  point  of  unvarying  tem- 
perature, both  for  day  and 
night  and  for  the  seasons,  is  little  more  than  a  foot  below  the 
surface.  Much  of  the  heat  received  by  the  soil  is  used  in 
evaporating  the  water  in  it.  For  this  reason  wet  soils  are 
cold  soils.  The  heat  used  in  evaporating  one  pound  of  water 
would  warm  7500  pounds  of  soil  one  degree.  Some  of  the 
heat  falling  on  the  earth  is  also  reflected  back  and  serves  to 
increase  the  temperature  of  the  air. 

Other  factors  that  modify  temperatures.  The  temperature 
of  the  soil  is  also  affected  by  its  color,  slope,  and  composition. 
Southern  slopes  are  warmer  than  northern  slopes  because  they 
receive  the  more  direct  rays  of  the  sun.   Soils  sheltered  from 


Fig. 


19.   Diagram  to  show  the  distri- 
bution of  the  sun's  rays 


When  the  sun  is  near  the  horizon,  the 

same  amount  of  heat  is  spread  over  a 

greater  area  than  when  it  is  overhead 


CONDITIONS  AFFECTING  SOIL  FERTILITY       43 

the  sun  in  any  way  are  cold ;  hence  the  saying,  "  There  is 
a  difference  of  100  miles  of  latitude  between  the  north  and 
south  sides  of  a  tight  board  fence."  The  fence  not  only  shuts 
off  the  heat  rays  from  one  side  of  it,  but  it  reflects  back  much 
heat  to  the  soil  on  the  other.  The  best  place  for  the  early 
vegetables  is  on  the  sunny  side  of  such  a  fence.  We  see  other 
effects  of  the  reflection  of  heat  in  our  greenhouses  and  hot- 
beds, where  the  air  under  the  glass  is  warmed  in  large  measure 
by  the  heat  reflected  back  from  the  soil.  Dry  soils  are  warmer 
than  wet  ones,  and  well-aerated  soils  are  warmer  than  those 
in  which  the  air  does  not  circulate  freely.  Color  also  influences 
the  amount  of  heat  absorbed  by  soils.  Black  soils  absorb  most, 
red  next,  yellow  next,  and  light  soils  least  of  all.  In  an  experi- 
ment with  two  samples  of  the  same  soil,  one  of  which  was 
whitened  with  magnesia  and  the  other  blackened  with  lamp- 
black, there  was  found  to  be  a  difference  of  more  than  12  de- 
grees in  favor  of  the  black  specimen.  A  soil  containing  much 
humus  is  warmer  than  one  that  lacks  it.  The  decay  of  or- 
ganic matter  adds  as  much  warmth  to  the  soil  as  would  be 
given  off  if  the  matter  were  burned  more  rapidly  in  the  air. 

The  Fahrenheit  and  centigrade  scales.  There  are  two  scales 
in  common  use  by  which  temperature  is  measured.  In  both, 
the  freezing  and  boiling  points  of  water  are  cardinal  points. 
The  Fahrenheit  scale  is  the  one  most  used  in  the  United  States 
at  present.  On  this  scale  zero  is  placed  32  degrees  below  the 
freezing  point  of  water,  and  the  boiling  point  180  degrees 
above  it,  making  212  degrees  between  zero  and  the  boiling 
point.  A  much  better  arrangement  is  found  in  the  centigrade 
scale,  where  the  freezing  point  of  water  is  called  zero  and 
the  distance  between  it  and  the  boiling  point  is  divided  into 
100  degrees.  A  degree  in  the  centigrade  scale  is  therefore 
larger  than  a  degree  Fahrenheit.  To  change  a  given  number, 
of  degrees  centigrade  to  Fahrenheit  one  must  multiply  by 
I  and  add  32  (C.  X  |  +  32  =  F.).    To  change  Fahrenheit  to 


44 


AGRONOMY 


centigratle,  subtract  32  and  multiply  by  |  (F.  —  32  x  |  =  C). 
Below  zero  centigrade  one  multiplies  by  |  and  subtracts  the 
product  from  32,  if  it  is  not  more  than  32.  If  more,  the  differ- 
ence between  this  and  32  mdicates  the  degrees  below  zero 
Fahrenheit.  If  the  temperatures  below  zero  Fahrenheit  are  to 
be  changed  to  centigrade,  atld  32  and  multiply  by  |.  The 
result  will  be  degrees  below  zero  centigrade.    In  all  cases 


Fig.  20.    ^Meau  annual  rainfall  in  the  United  States 
From  Brigham's  "  Commercial  Geography  " 

where  temperatures  are  recorded  without  the  scale  indicated, 
as  in  this  book,  it  is  underetood  to  refer  to  the  Fahrenheit 
scale.  The  centigrade  scale,  however,  has  found  favor  with 
scientific  men,  and  it  is  probable  that  in  the  near  future  it 
will  supplant  the  other. 

Precipitation.  The  most  important  function  of  the  soil  is  to 
afford  water  for  plants.  In  many  parts  of  the  West  thousands 
of  acres  are  barren  and  useless  for  want  of  this  indispensable 
factor.  When  it  is  applied  to  the  soil  in  irrigation,  the  desert 
at  once  becomes  a  garden.    Precipitation  may  occur  as  rain, 


CONDITIONS  AFFECTING  SOIL  FERTILITY       45 

snow,  hail,  or  dew,  and  varies  with  the  locahty  and  season, 
being  usually  greatest  near  coasts  where  moisture-laden  winds 
blow  inland,  and  least  where  the  prevailing  wmds  blow  in  the 
opposite  direction.  On  parts  of  the  Gulf  coast  the  annual  rain- 
fall is  about  70  inches,  on  the  northwest  coast  it  may  be  from 
105  to  112  inches.  In  the  Mojave  desert,  surrounded  by  moun- 
tains that  intercept  the  moisture,  it  is  less  than  2  inches  a  year. 


PRECIPITATION   AT    JoLIKT,    ILLINOIS,    FOK    FOUU    YkARS 
ILLUSTRATING    VARIATIONS    THAT    MAY    OCCUR 


Month 

January    .  .     . 

February  .  .     . 

March  .     .  .     . 

April    .     .  .     , 

May      .     .  .     , 

June      .     .  .     . 

July      .     .  .     . 

August      .  .     , 

September  .     , 

October     .  .     . 

November  .     , 

December  .     , 

^  Annual    .  . 


1908 


.77 
2.66 
4.33 
3.32 
6.95 
1.30 
3.79 
3.80 
1.32 

.82 
2.77 
1.30 


33.13 


1909 


1.12 

3.38 
1..56 
6.60 
3.46 
•3.80 
1.69 
2.95 
3.09 
1.68 
4.55 
3.50 


37.38 


1910 


2.52 
2.45 

.24 
3.81 
4.90 

.81 
1.46 
3.17 
2.75 
1.68 

.62 
1.12 


25.53 


1911 


1.58 
1.62 
1.39 
4.45 
3.65 
4.65 
2.46 
4.54 
12.27 
4.18 
2.87 
1.91 


45.57 


The  heaviest  rainfall  in  the  world  is  found  in  the  Khasi  hills, 
north  of  the  Bay  of  Bengal,  where  the  precipitation  may  reach 
600  inches  a  year.  More  than  40  inches  have  fallen  in  a  single 
day  there.  The  rainfall  of  the  United  States  seems  generally 
to  increase  as  one  goes  eastward.  Over  much  of  the  Rocky 
Mountain  region  it  is  from  10  to  20  inches,  on  the  western 
edge  of  the  Great  Plains  it  is  from  20  to  30  inches,  in  the  north- 
central  states  it  is  from  30  to  40  inches,  and  the  eastern  states 

1  The  average  annual  precipitation  at  this  station  for  eighteen  yeare  is  34.58 
inches. 


46 


AGKONOMY 


have  from  40  to  50  inches.  Over  most  of  the  Gulf  states  the 
rainfall  is  from  50  to  60  inches.  About  215,000,000,000,000 
cubic  feet  of  water  fall  annually  in  the  United  States.  This 
would  cover  5,000,000,000  acres  a  foot  deep,  or  keep  ten 
Mississippi  rivers  constantly  flowing.  In  figuring  precipita- 
tion, 10  inches  of  snow  are  considered  equal  to  1  inch  of  rain. 
Dew  may  form  within  the  soil  as  well  as  upon  it,  but  the 
amount  of  moisture  added  in  this  way  is  negligible.    Dry  soils 


Photograph  by  H.  L.  HoUister  Laud  Co. 


Fig.  21.    Sagebrush  on  the  Western  plains 

The  rainfall  is  insufficient  for  cultivated  crops,  but  when  irrigated  tlie  lan'd 
yields  abundant  harvests 

are  also  able  to  absorb  moisture  from  damp  air,  the  moisture 
condensing  upon  the  soil  particles.  Sands  absorb  least  and 
humus  most.  Quicklime  slakes  when  exposed  to  the  air,  by 
absorbing  moisture  in  this  way.  So  strong  is  this  tendency 
of  quicklime  to  absorb  moisture  that  the  chemist  uses  it  to 
dry  the  air  used  in  various  experiments.  A  fine  soil  will  also 
absorb  moisture  from  a  coarser  one.  Clay  may  sometimes  take 
water  from  sand,  though  the  latter  may  contain  less  moisture 
than  the  clay. 


CONDITIONS  AFFECTING  SOIL  FERTILITY       47 

Water  in  the  soiL  A  part  of  the  water  which  falls  in  rain 
immediately  evaporates,  a  part  sinks  into  the  soil,  and  the  rest 
drains  away  into  streams  and  ponds.  This  latter  is  known  as 
the  run-off.  The  water  that  sinks  into  the  soil  is  called  the 
percolating  water.  The  run-off  is  greater  in  clay  than  in  sand, 
on  slopes  than  on  the  level,  and  in  cultivated  soil  than  in 
pasture  or  woodland.  Clay  gullies  more  easily  than  sand  be- 
cause the  water  cannot  penetrate  it  so  readily.  Pastures  and 
woodlands  protected  by  the  close  ground  cover  are  scarcely 
affected  by  a  rain  that  may  wash  out  the  crops  in  cultivated 
fields.  The  water  that  enters  the  soil  exists  there  in  three 
forms,  known  as  free,  capillary,  and  hygroscopic  water.  Free 
water  responds  to  the  pull  of  gravity  and  goes  downward  until 
it  reaches  a  point  where  the  soil  is  saturated.  Capillary  water 
is  not  affected  by  gravity,  but  moves  from  moist  to  dry  regions 
like  a  drop  of  water  on  blotting  paper  or  the  oil  in  a  lamp 
wick.  Much  dissolved  plant  food  is  brought  up  from  the  sub- 
soil by  the  capillary  water,  and  the  alkali  in  certain  soils  is 
due  to  the  same  cause.  Hygroscopic  water  is  not  affected  by 
either  gravity  or  dryness.  It  clings  closely  to  the  soil  particles 
and  binds  them  into  soil  crumbs.  It  is  present  even  in  air-dry 
soils  and  roadside  dust,  but  is  not  available  to  plants.  Plants 
depend  largely  for  their  moisture  on  the  capillary  water  in  the 
upper  layers  of  soil,  though  some  of  the  free  water  deeper  m 
the  earth  may  return  by  capillarity.  Water  rises  highest  by 
capillarity  in  fine-grained  soils.  Clays  and  silts  can  lift  water 
in  this  way  from  six  to  ten  feet.  In  sandy  soils  water  will 
not  rise  more  than  two  feet. 

The  water  table.  The  free  water  sinks  downward  until  it 
reaches  a  point  where  all  the  spaces  between  the  particles  are 
filled  with  water,  or  where,  as  we  say,  the  soil  is  saturated. 
This  point  is  known  as  the  water  table,  or  permanent  ground 
water.  It  now  spreads  out  laterally  and  slowly  drains  off  by 
seeping  out  of  the  soil  at  the  edge  of  streams,  lakes,   and 


48 


AGRONOMY 


swamps,  or  perhaps  it  may  come  to  the  surface,  f ormmg  springs. 
In  certain  seasons,  or  in  places  wliere  there  is  a  stratum  of 
impervious  subsoil,  there  may  be  saturated  areas  above  the 
water  table  that  will  cause  tile  drains  to  run.  The  real  water 
table,  however,  lies  deeper.  It  varies  with  the  rainfall,  rising 
in  wet  seasons  and  falling  in  dry  ones.    We  dig  our  ordinary 


Photograph  by  II.  L.  Hollister  Land  Co. 

Fig.  22.    One  of  the  main  laterals,  or  branches,  of  an  irrigation  canal 
From  this  stream  smaller  channels  lead  to  the  separate  fields 

wells  down  into  it,  and  in  dry  seasons  they  may  dry  up,  owing 
to  the  lowering  of  the  water  table.  The  fluctuating  water 
level  may  sometimes  affect  the  character  of  mineral  springs 
flowing  from  it,  giving  them  an  excess  first  of  one  mineral 
and  then  of  another  as  the  water  comes  in  contact  with  differ- 
ent rock  strata.  Above  ground  a  water  surface  is  level,  but 
in  earth  the  water  table  curves  upward  under  liills  chiefly 
because  the  soil  retards  the  downward  progress  of  the  free 


CONDITIONS  AFFECTING  SOIL  FERTILITY       49 


water  after  a  rain.  Ponds  and  marshes  are  usually  at  the 
level  of  the  water  table. 

Drainage.  In  the  eastern  United  States  it  is  estimated  that 
there  are  a  hundred  million  acres  of  swamp  that  could  be 
rendered  useful  by  drainage.  All  soils  have  to  be  drained 
before  cultivated  crops  can  be  grown  in  them.  The  majority 
are  drained  naturally.  Sand  is  often  too  well  drained.  When 
the  saturated  con- 
dition of  the  soil 
results  from  the 
seepage  of  water 
from  higher  levels, 
tile  drains  may  be 
used  to  carry  it 
away,  but  when 
the  land  lies  very 
little  above  the  nat- 
ural drainage,  tile 
drains  would  be 
useless  and  open 
ditches  must  take 
their  place.  Lands 
that  are  not  per- 
manently wet  are 
often  benefited  by 
tile  draining.   The 

removal  of  the  surplus  water  deepens  the  area  into  which 
the  roots  of  plants  can  spread,  warms  the  soil  by  admitting 
the  air,  and  promotes  further  weathering  of  the  subsoil. 
Draining  wet  lands  may  actually  give  the  plants  more  water 
by  increasing  the  area  from  which  the  roots  can  absorb, 
thus  making  them  more  drought-resistant.  Drainage  also 
makes  it  possible  to  begin  the  work  on  wet  lands  earlier  in 
the  spring. 


Plioto^'raph  by  H.  L.  IloUister  Land  Co. 

Fig.  23.    A  check  gate  in  an  irrigation  ditch 

This  holds  back  the  water  and  causes  it  to  flow 
through  smaller  channels  into  the  fields 


AGRONOMY 


Photograph  by  Mark  Bennitt 

Fig.  24.    A  field  of  wheat  in  tlie  dry-farming  region 


Fig.  25.  "Irrigating  a  fig  orcliard  in  California 


'o^^'^o  "  "o 


Irrigation.  Ordinary  crops  can  be  produced  with  as  little 
as  twenty  inches  of  rainfall  if  it  is  properly  distributed,  but 
when  it  does  not  come  in  the  growing  season,  or  is  limited  in 


CONDITIONS  AFFECTING  SOIL  FERTILITY       51 

amount,  the  lands  must  be  irrigated  if  crops  are  to  be  grown. 
Many  otherwise  sterile  soils  are  very  fertile  when  water  is 
applied.   Irrigation,  however,  can  be  carried  on  only  when  the 


13  in. 

1 \ ^ ^ 1 

Total  1911  45.57 

Total  1910  25.53 

12  in. 

A 

1 

v.4y 

•s.  35. 

W 

11  In. 

10  in. 

9  in. 

Sin. 

Tin. 

I 
/ 

Gin. 

; 
1 

5  in. 

1 

4  in. 

^ 

V 

'\ 

/ 

/ 

, 

3  in. 

// 

/    ^., 

'\\ 

\ 

/ 

/ 

^,^ 

2  in. 

/ 

^ 

N^ 

/'  / 

r 

^ 

7 

^ 

\\ 

^ 

^v^ 

1  in. 

/^ 

A~ 

\   > 

/ 

\ 

y 

/ 

\ 

\ 

1911 
_1910 

/yan. 

Feb. 

Mar. 

Apr. 

May 

June 

July 

Aug. 

Sept. 

Oct. 

\ 

Nov. 

Dec. 

Fig.  26.   Precipitation  at  Joliet,  Illinois 

The  heavy  line  represents  the  average  for  the  years  1908,  1909,  1910,  and  1911. 
See  page  45  for  the  precipitation  by  months.    (Data  supplied  by  F.  M.  Muhlig, 

United  States  Weather  Observer) 

land  is  properly  located  with  reference  to  a  permanent  source  of 
water  supply.  Usually  some  near-by  lake  or  stream  is  selected, 
a  dam  built  across  it,  and  the  water  which  falls  in  its  basin 
stored  for  the  use  of  the  crops.  From  the  dam,  canals  are  made 
to  run  through  the  lands  to  be  irrigated,  and  smaller  ditches, 


52 


AGRONOMY 


into  which  the  water  may  be  turned  as  needed,  traverse  the 
fields.  Crops  on  irrigated  land  are  usually  certain,  since  the 
farmer  is  relieved  from  any  dependence  on  the  natural  rainfall. 
Dry  farming.  Twenty  inches  of  rainfall,  properly  distrib- 
uted, is  about  the  minimum  amount  that  will  produce  ordinary 
crops.  In  a  few  localities,  where  the  rainfall  is  less,  crops  are 
produced  by  a  system  of  dry  farming  in  which  the  scanty 
moisture  is  stored  up  in  the  soil  until  there  is  sufficient  for  a 


Tin. 

Gin. 

/ 

\ 

5  in. 

/ 

\ 

4  in. 

/ 

\ 

J 

\^ 

Sin. 

/ 

\, 

/ 

\ 

^ 

\ 

/ 

N 

2  in. 

/ 

\ 

\ 

/ 

\ 

/ 

1  in. 

/ 

\ 

/ 

\ 

/ 

s 

/Uan. 

Feb. 

Mar. 

Apr. 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Fig.  27.  Diagram  showing  precipitation  at  Joliet,  Illinois,  in  1909 
Data  supplied  by  F.  M.  Muhlig,  United  States  Weather  Observer 

crop.  This  method  consists  in  keeping  the  surface  of  the  soil 
constantly  loose,  partly  for  the  purpose  of  absorbing  all  the 
rain  that  falls,  partly  to  prevent  the  evaporation  of  the  water 
already  in  the  soil.  A  crop  may  thus  be  grown  every  other 
year,  or  two  crops  in  three  years,  the  land  remaining  without 
a  crop,  though  carefully  tilled,  during  the  intervening  time. 
Crops  have  been  grown  by  this  method  in  regions  where  the 
rainfall  is  but  twelve  inches.  In  some  cases  it  is  possible  to 
get  a  crop  annually  by  cultivating  the  soil  during  that  part 
of  the  year  when  it  is  not  occupied  by  plants.  The  selection 
of  drought-resistant  plants  may  also  facilitate  dry  farming. 


I 


CO:^^DITIONS  AFFECTING  SOIL  FERTILITY       63 

Physiologically  dry  soils.  A  physically  dry  soil  is  one  in 
which  there  is  no  moisture,  but  even  in  a  soil  containing  much 
water,  if  the  plants  are  unable  to  absorb  it,  it  is  physiologically 
dry  to  them.  In  winter,  though  the  soil  may  be  saturated,  it 
is  physiologically  dry  because  the  moisture  is  locked  up  in  the 
form  of  ice.  Strong  salts  or  acids  of  any  kind  in  the  water 
may  also  prevent  absorption.  It  is  probable  that  many  plants 
which  grow  in  bogs  find  the  soil  physiologically  dry  to  them, 
though  at  the  same  time  it  may  be  soaked  with  water. 

PRACTICAL  EXERCISES 

1.  Take  two  bottles  of  equal  size  and  fill  with  roily  water  made  by- 
shaking  up  some  clay  with  rain  water  or  distilled  water.  Add  to  one 
bottle  one  tenth  its  bulk  of  a  solution  of  lime  and  water  and  stand  both 
bottles  where  they  will  not  be  disturbed.  Examine  at  intervals  to  see 
which  settles  first,  and  explain  the  result. 

2.  Weigh  out  three  samples  of  clay  of  200  g.  each.  To  one  add 
10  g.  of  slaked  lime,  to  another  add  10  g.  of  sand,  and  to  the  third  add 
10  g.  more  of  the  clay.  Add  enough  water  to  make  plastic  and  form 
into  three  balls.  When  these  are  thoroughly  dry,  pile  weights,  little  by 
little,  upon  each  until  it  is  crushed.  Explain  the  different  effects  of 
sand  and  lime. 

3.  Take  four  straight-sided  lamp  chimneys  and  fill  one  each  with 
sand,  clay,  peat,  and  soil  from  the  school  garden.  These  materials 
should  all  be  dry  and  well  pulverized.  Tie  a  piece  of  cheesecloth  over 
the  bottom  end  of  each  chimney  and  stand  them  in  a  rack,  with  the 
bottoms  dipping  into  a  shallow  pan  of  water.  In  which  does  the  water 
rise  most  rapidly?  In  which  most  slowly?  Do  you  conclude  that  in 
drying  they  would  follow  the  same  order  ?   Try  it  and  see. 

4.  Visit  the  nearest  barometer  and  barograph  to  learn  how  the 
pressure  of  the  air  is  measured  and  recorded.  Examine  both  centigrade 
and  Fahrenheit  thermometers. 

5. ,  Fill  a  glass  with  water,  lay  a  sheet  of  writing  paper  over  it,  and 
holding  the  paper  in  place,  quickly  invert  the  glass.  When  the  hand  is 
removed,  why  does  the  water  not  nm  out  ? 

6.  Light  a  piece  of  paper,  thrust  it  into  a  glass  jar,  and  invert  the 
jar  in  a  shallow  dish  of  water.  Explain  the  action  that  takes  place  in 
the  water. 


64  AGKONOMY 

7.  Select  two  thermometers  graduated  alike  and  place  them  so  that 
their  bulbs  only  will  be  exposed  to  the  sun.  Cover  one  bulb  with  a 
white  cloth  and  the  other  with  a  black  one.  Which  thermometer  now 
measures  higher  ?    How  much  ?   Explain. 

8.  Take  the  two  thermometers  and  cover  both  bullis  with  the  same 
kind  of  cloth.  Wet  one  cloth  and  leave  the  other  dry.  What  difference 
do  you  now  find  in  the  way  they  register  ?  Explain.  Does  fanning  them 
have  any  effect  upon  the  temperature  registered  ? 

9.  Change  40° C.  to  Fahrenheit;  60°;  85°. 

10.  Change  68°  F.  to  centigrade ;  95°;  41°. 

11.  From  the  nearest  weather  observer  find  the  average  rainfall  by 
months  for  the  past  five  years.  Plot  the  curve  for  the  year  as  in 
Fig.  26,  p.  51.  The  numbers  at  the  left  indicate  the  amount  of  rain- 
fall in  inches.    What  is.  the  average  annual  rainfall  of  your  region  ? 

12.  Plot  the  rainfall  curve  for  the  present  year  or  for  the  preceding 
one.    Is  the  rainfall  well  distributed  through  the  growing  season? 

13.  ISIake  a  similar  curve  for  the  average  temperature  by  months 
for  the  past  five  years. 

14.  In  a  rainfall  of  half  an  inch  how  many  cubic  inches  fall  on  an 
acre  of  ground  ?  how  many  gallons  ?  how  many  barrels  ?  How  many 
gallons  fall  on  the  school  garden  ?   on  your  own  plot  in  it  ? 

15.  What  is  the  total  amount  of  water  that  fell  on  the  school  gar- 
den last  month  ? 

16.  If  an  acre  of  ground  is  half  pore  space,  how  many  gallons  of 
water  will  be  contained  in  the  upper  7  in.  when  the  soil  is  saturated  ?. 

17.  From  wells  in  the  vicinity  ascertain  how  far  below  the  surface 
the  water  table  lies. 

18.  Visit  a  marsh,  hillside,  or  ledge  of  rocks,  and  decide  what  causes 
the  water  table  to  come  to  the  surface  here. 

19.  Visit  lands  that  have  been  tile  drained.  Are  there  any  other 
lands  in  the  vicinity  that  would'  be  benefited  by  the  same  treatment  V 
Are  there  any  lands  that  open  ditches  would  serve  better?  any  land 
where  irrigation  could  be  practiced  to  advantage  ? 

References 

Fanners'  Bulletins 

46.  Irrigation  in  Humid  Climates. 
138.  Irrigation  in  Field  and  Garden. 
187.  Drainage  of  Farm  Lands. 
263.  Practical  Information  in  Irrigation. 
371.  Drainage  of  Irrigated  Lands. 


CHAPTER  V 


THE  ORGANIZATION  OF  THE  PLANT 

The  great  plant  groups.  The  vegetation  of  the  earth  con- 
sists of  a  bewildering  variety  of  forms.  At  one  extreme 
are  plants  consist- 
ing of  a  single  cell 
and  therefore  lack- 
ing roots,  stems, 
leaves,  flowers,  or 
fruits ;  at  the  other 
are  the  great  trees, 
like  the  giant  red- 
woods and  euca- 
lypti, which  tower 
to  the  height  of 
hundreds  of  feet 
and  spread  millions 
of  leaves  to  the  sun- 
shine. Some  spe- 
cies are  adapted  to 
live  in  ponds  and 
streams,  and  spend 
their  whole  life  im- 
mersed in  water ; 
others  inhabit  des- 
erts in  which  rain 
rarely  falls  and 
moisture  is  at  the 


Fig.  28.    Pteridgphytes.    A  colony  of  walking 
ferns  (Camptosorus) 


minimum.  Between  these  extremes  all  sorts  of  vegetable  forms 
occur.  Herbs,  shrubs,  vines,  and  trees  vie  with  one  another  for 

55 


66 


AGRONOMY 


---cyto 


a  roothold  and  access  to  the  light  and  air,  while  mosses,  ferns, 
and  fungi  grow  among  and  upon  them.  This  great  diversity 
of  form  makes  it  necessary  to  place  the  plants  in  different 
groups,  according  to  their  common  characteristics,  and  bota- 
nists generally  make  four  great  groups  of  this  kind.  First  and 
simplest  in  structure  are  the  Thallophytes^  comprising  the  algae, 
fungi,  and  bacteria.  None  of  these  have  true  leaves  or  stems, 
or  produce  either  flowers  or  fruits.  Next  above  these  come 
the  BryophyteB,  which  include  the  mosses  and  liverworts. 
They  are  somewhat  more  liighly  organ- 
ized than  the  thallophytes,  but  are  like 
them  in  lacking  true  leaves,  flowers, 
and  fruits.  The  Pteridophyfes  consist  of 
the  ferns  and  their  allies.  These  plants 
have  stems  and  leaves,  and  some  spe- 
cies bear  structures  that  are  essentially 
flowers,  but  none  bear  seeds.  Last  and 
most  highly  specialized  are  the  Sj^er- 
matophytes,  or  true  flowering  plants, 
which  are  distinguished  from  all  the 
others  by  the  production  of  seeds. 

Only  two  of  these  groups  are  of 
much  interest  to  the  farmer  and  gar- 
dener. The  thallophytes  have  to  be 
taken  into  account  because  from  their 
ranks  come  not  only  the  bacteria  that 
flavor  cheese,  butter,  and  other  prod- 
ucts, turn  cider  to  vinegar,  and  render 
soils  fertile,  but  also  the  multitudes 
of  plant  diseases  and  fungus  pests  that  injure  the  cultivated 
crops,  destroy  our  foods,  cause  disease  in  the  lower  animals, 
and  even  attack  man  himself.  The  cultivated  plants,  however, 
are  spermatophytes,  and  so  are  the  weeds  that  struggle  with 
them  for  the  possession  of  the  soil.    The  word  spermatophyte 


3- — cell  w 


Fig.  29.  An  epidermal  hair 

from  the  bi^acken  showing 

the  cells 

cell  w,  cell  wall ;  cyto,  cyto- 
plasm; uu,  nucleus;  s,  starch 
grains 


THE  ORGANIZATION  OF  THE  PLANT  57 

means  "  seed  plant,"  and  this  name  was  given  to  the  highest 
group  of  plants  in  recognition  of  the  way  in  which  they  are 
reproduced.  All  the  other  groups  are  developed  from  tiny 
one-celled  structures  called  spores.  These  are  individually 
too  small  to  be  seen  with  the  unaided  eye,  but  in  masses  are 
recognized  as  the  black  mold  on  bread,  the  smoke  from  puff- 
balls,  and  the  like. 

The  regions  of  the  plant.  A  typical  flowering  plant  is 
often  said  to  consist  of  root  and  shoot.  The  stem,  however, 
is  the  real  axis  of  the  plant  and  bears  all  the  other  organs.  It 
is  present  in  the  seed,  and  the  first  root  grows  from  it ;  in- 
deed, roots  normally  grow  from  stems,  not  stems  from  roots, 
as  is  popularly  supposed.  The  root  grows  downward  m  the 
soil,  holding  the  plant  in  place  and  absorbing  necessary  mois- 
ture and  minerals.  The  shoot  pushes  up  into  the  air  from 
which  it  takes  other  necessary  food  material.  In  the  leaves 
and  other  green  parts  of  the  plant  these  materials  from  both 
the  earth  and  air  are  ultimately  combined  to  form  plant  food 
by  means  of  energy  derived  from  sunlight.  After  a  store  of 
plant  food  is  secured,  flowers  appear,  and  seeds  are  formed 
for  the  purpose  of  reproducing,  niultiplying,  and  distributing 
the  species.  These  two  functions,  growth  and  reproduction, 
are  common  to  all  plants.  During  the  early  part  of  their 
existence  the  growth  processes  are  in  the  ascendant ;  later, 
reproductive  functions  prevail. 

Cellular  structure  of  the  plant.  All  parts  of  the  plant  are 
formed  of  mmute  boxlike  structures  called  cells,  which  are 
usually  much  too  small  to  be  seen  without  the  aid  of  the  mi- 
croscope. The  ordinary  undifferentiated  cell  consists  of  a  semi- 
fluid, nearly  transparent  substance  cdXledi  protoplasm  surrounded 
by  a  thin  membrane  known  as  the  cell  wall.  Within  the  proto- 
plasm are  one  or  more  spaces  called  vacuoles  containing  a 
watery  fluid,  the  cell  sap.  Somewhere  in  the  protoplasm,  also, 
usually  at  one  side  of  the  cell,  is  a  denser,  darker  part  called 


58 


AGRONOMY 


the  nucleus.  The  nucleus  is  the  center  of  the  cell's  activities. 
When  a  new  cell  is  to  be  formed,  the  nucleus  first  divides 
mto  two  equal  parts  and  then  the  division  extends  outward 

to  the  surrounduig  cell 
wall.    Soon  there  are 
two  new  cells  in  place 
of    the    original    one, 
new  walls  having  been 
constructed     between 
them.  These  two  cells 
now  grow  to  maturity 
and  are  ready  to  re- 
peat the  process.    All 
growth  is  essentially  like  this.    When  growing  alone,  the  cell 
inclines  to  take  a  spherical  shape,  but  in  plant  and  animal  tis- 
sues, where  it  is  crowded  on  all  sides,  it  becomes  more  or  less 


Fig 


30.    Cells  with  nuclei  from  the  epidermis 
of  the  onion  bulb 


f 

^^^^- 

"^aP^^^^I 

M 

1 

■ 

■1 

-I '  „■*  ^  ^ 

n 

mm 

i 

^ 

|te-^SWI|LMfti<^^^?i 

foH 

IMIII 

11 

I^K 

HnH 

V^K^^HI 

H 

1 

I 

H 

Photograph  by  the  United  States  Department  of  Agriculture 

Fig.  31.   The  root  system  of  the  corn  plant 

angular.  The  cells  in  the  woody  parts  of  plants,  in  bark  and 
the  like,  are  very  different  from  the  cell  just  described,  but 
all  began  as  cells  of  this  kind. 


THE  ORGANIZATION  OF  THE  PLANT 


59 


Roots.  The  root,  or  underground  portion,  of  the  plant  is 
the  first  to  put  forth  from  the  germinating  seed.  No  matter 
in  what  position  the  seed  may  happen  to  be  lying  when  growth 
begins,  the  root,  in  response  to  gravity,  tends  to  grow  straight 
downward,  often  curving  considerably  to  do  so.  This  is  of 
great  advantage  to  the  young  plant,  since  it  quickly  brings 
it  into  contact  with  the  neces- 
sary moisture  and  other  food 
materials,  and  also  gives  it  a 
hold  in  the  soil.  The  root,  how- 
ever, is  not  pulled  down  by 
gravity,  but  simply  uses  this 
force  as  a  guide.  After  reach- 
ing the  soil  it  may  turn  aside 
for  moisture  or  food  materials, 
or  to  avoid  obstacles,  such  as 
stones,  in  the  soil.  In  its  search 
for  moisture  it  often  goes 
long  distances.  Instances  are 
known  where  the  roots  of  a 
tree  have  in  tliis  way  filled 
drains  three  hvmdred  feet  away. 
Soon  after  penetrating  the  soil 
the  first  root  begins  to  give 
off  branches,  and  these  branch 
and  branch  again,  spreading 
out  laterally  and  thoroughly  exploring  the  soil  for  food  mate- 
rials. These  lateral  roots  are  often  very  numerous.  A  single 
corn  plant  may  have  enough  roots  to  measure  a  quarter  of  a 
mile  or  more  when  placed  end  to  end.  In  humid  regions 
roots  seldom  descend  more  than  four  or  five  feet,  but  in  arid 
regions  they  may  go  much  deeper.  The  main  root  of  such 
plants  as  mesquite,  shepherdia,  and  alfalfa  have  been  known 
to  go  down  fifty  or  sixty  feet  in  search  of  moisture. 


Fig.  32.    Wild  hyacinth  {Camassia) 
with  multiple  primary  roots 


GO 


AGRONOMY 


Taproots.  In  a  large  number  of  species  the  main  root 
continues  to  grow,  becoming  the  main  axis  of  the  plant- 
underground.    Such  a  root   is  called  a  taproot.    Frequently 

the  taproot  is  used  for  the  storage 
of  food  and  is  often  much  enlarged 
for  this  purpose.  Good  examples  of 
taproots  may  be  seen  in  the  carrot, 
parsnip,  and  dandelion.  All  our  root 
crops  are  cultivated  for  the  food 
stored  by  the  plant  in  the  main  or 
lateral  roots.  In  some  plants  the 
first  root  fails  to  keep  ahead  of  the 
others,  and  no  taproot  is  found  in 
mature  specimens.  The  root  system 
of  the  corn  illustrates  this.  The 
onion,  hyacinth,  and  other  lily  like 
plants  exhibit  good  examples  of 
what  are  called  multiple  primary 
roots,  where  several  roots  of  equal 
size  arise  together  from  the  base  of 
the  stem.  Plants  with  taproots  are 
said  to  have  an  axial  root  system ; 
without  a  taproot  it  is  inaxial. 
Structure  of  the  root.  The  young  roots  of  plants  are  alike 
in  all  essential  particulars.  In  the  center  is  a  somewhat  fibrous 
portion  known  as  the  central  cylinder,  and  surrounding  it  is  a 
softer  layer,  the  cortex.  On  the  outside  is  a  thin  skin  formed 
of  waterproof  cells,  which  is  known  as  the  epidermis.  The 
central  cylmder  has  a  series  of  small  tubes,  or  ducts,  running 
lengthwise  tlu-ough  it,  and  it  is  along  these  ducts  that  the 
water  absorbed  by  the  plant  travels  upward.  Roots  that 
continue  to  live  for  some  years,  annually  spreading  into 
wider  territory  and  absorbing  a  greater  amount  of  food  mate- 
rial, need   a  larger  number  of  ducts  for  transporting  these 


Fig.   33,     Taproot    of    the 
parsnip 

The  sectional  specimen  shows 
the  central  cylinder  and  cortex 


THE  ORGANIZATION  OF  THE  PLANT 


61 


substances.  The  new  ducts  are  provided  by  a  ring  of  growing 
cells,  called  cambium  cells,  that  originate  just  inside  the  cor- 
tex and  encircle  the  central  cylinder.  The  cambium  may  also 
add  other  fibrous  and  corky  cells  to  the  cortex,  and  in  time 
these  form  the  bark  seen  in  the  roots  of  old  trees.  The  activi- 
ties of  the  cambium,  therefore,  result  in  increasing  the  diam- 
eter of  the  root  from  year  to  year,  but  growth  in  length  takes 
place  at  the  tip  of  the 
root  only,  and  never  at 
the  base,  as  is  generally 
supposed.  If  growth  in 
length  occurred  at  the 
base  of  the  root  instead 
of  at  the  tip,  the  whole 
root  would  have  to  be 
pushed  through  the  soil, 
a  task  which  the  plant 
would  soon  find  impossi- 
ble of  accomplishment. 

In  the  wild  state  the 
seeds  of  plants  are  scat- 
tered on  the  surface  of 
the  soil  and  germinate 
without  getting  very  far 
below  it,  but  at  maturity 
we  commonly  find  the 
base  of  the  stem,  or  even  the  whole  stem,  some  distance 
underground.  In  many  cases  this  burial  of  the  stem  is  due 
to  the  contraction  of  the  roots.  These  penetrate  the  soil, 
and,  after  becoming  established,  contract  and  pull  the  plant 
downward.  The  contraction  is  mainly  in  the  central  cylinder 
and  results  in  wrinkling  the  cortex.  Such  contraction  wrm- 
kles  are  well  shown  in  the  roots  of  the  skunk  cabbage  or 
the  ii'is. 


Fig.  34.    Enlarged  cross  section  of  a  young 

root  showing  epidermis,  cortex,  and  central 

cylinder 

The  large  openings  in  the  central  cylinder  are 

the  ducts.    Note  the  root  liairs  growing  from 

the  epidermis 


62 


AGRONOMY 


Root  hairs.  Roots  do  not  absorb  through  all  parts  of  theu* 
surface,  as  is  commonly  supposed.  The  waterproof  epidermis 
prevents  the  passage  of  moisture  tlirough  all  the  older  parts, 
and  only  a  small  portion  near  the  tip,  where  there  are  special 

structures,  called  root  hairs,  de- 
signed for  the  purpose,  is  able  to 
perform  this  office  for  the  plant. 
At  first  glance  a  waterproof  epi- 
dermis might  seem  a  disadvantage 
to  the  plant,  but  its  utility  is  seen 
when  we  learn  that  it  serves  to 
prevent  moisture  once  absorbed 
from  passing  out  into  the  soil 
again.  The  root  hairs  are  tiny 
tubes  closed  at  the  end,  which 
project  from  a  zone  of  epidermal 
cells  just  back  of  the  root  tip.  As 
the  root  adds  to  its  length,  new 
root  hairs  are  developed  on  the  side  of  the  zone  toward  the 
growing  point,  while  on  the  other  the  old  ones  slowly  shrivel 
and  disappear.  The  advancing  root  is  thus  always  provided 
with  a  zone  of  fresh  root  hau's  with  which  to  absorb.  On 
seedlings  that  have  been 
sprouted  in  moist  air  the 
root  hairs  appear  like  a 
fme  white  down.  They  are 
very  numerous  and  spread 
out  in  all  directions  among 
the  soil  particles,  affording 
a  much  larger  surface  for 
absorption  than  would  the  epidermal  cells  alone.  As  the  roots 
push  onward  through  the  soil  the  development  of  fresh  root 
hairs  constantly  brings  the  plant  into  contact  with  new  sources 
of  food  materials. 


Fig.  35.  A  bit  of  epidermis  with 
young  root  hairs.   (Enlarged) 


Fig.  3G.    A  single  root  hair  projecting 
from  an  epidermal  cell.   (Much  enlarged) 


THE  OEGANIZATION  OF  THE  PLAJ^T  63 

Osmosis.  Root  hairs  absorb  from  the  soil  by  a  physical 
process  known  as  osmosis.  In  this,  when  two  liquids  of  different 
densities  are  separated  by  a  membrane,  such  as  a  cell  wall  and 
its  lining  of  protoplasm,  there  is  at  once  set  up  a  tendency  for 
each  liquid  to  pass  through  the  membrane  to  the  other  until 
both  liquids  are  of  equal  density.  In  osmosis  the  current  from 
the  less  dense  liquid  into  the  denser  is  always  the  stronger. 
One  can  illustrate  the  process  very  well  by  filling  a  small  jar 
with  molasses  and  tying  a  piece  of  parclmtient  paper  or  hog's 
bladder  over  the  open  end  to  represent  a  cell,  and  immersing 
this  jar  in  a  larger  jar  of  clear  water  for  a  few  hours.  If  care 
has  been  taken  to  make  a  water-tight  joint  between  the  jar  and 
its  parchment  cover,  sufficient  clear  water  will  pass  through 
the  membrane  into  the  molasses  to  distend  the  covering  of  the 
jar  to  its  utmost.  In  the  plant  the  evaporation  of  water  from 
the  leaves  or  its  use  in  forming  plant  food  renders  the  sap  in 
the  cells  more  dense  than  the  soil  water,  and  this  consequently 
flows  into  the  plant,  carrying  the  dissolved  minerals  with  it  as 
these  processes  continue.  Once  in  the  root,  the  water  spreads 
from  cell  to  cell  through  the  cortex  until  it  finally  reaches  the 
ducts  in  the  central  cylinder  and  is  sent  upward  to  the  shoot. 
The  root  hairs  not  only  absorb  the  water  that  clings  to  the 
soil  particles  with  which  they  come  in  contact,  but  this  absorp- 
tion sets  up  a  capillary  movement  which  drains  adjacent  parti- 
cles of  their  moisture.  If  there  should  happen  to  be  a  large 
enough  amount  of  any  soluble  substance  in  the  soil,  the  cur- 
rent of  water  would  set  outward  from  the  plant  and  cause  its 
death.  This  is  what  happens  when  we  put  salt  upon  weeds 
or  grass,  and  explains  why  ordinary  plants  cannot  live  in 
alkali  soils. 

The  stem.  For  convenience  the  shoot  may  be  divided  into 
stem  and  leaves.  The  flowers,  which  at  first  might  appear  to 
belong  to  a  third  division,  are  really  homologous  with  leaves 
and  frequently  show  the  relationship  by  becoming  leaflike. 


G4 


AGRONOMY 


In  the  green  rose  all  the  petals  of  the  flower  revert  to  leaves. 
Stems  are  of  most  varied  forms :  in  forest  trees,  tall,  strong, 

and  enduring  for  cen- 
turies ;  m  the  herbs, 
low,  weak,  and  lasting 
but  a  single  season. 
In  the  crocus  the  stem 
is  reduced  to  a  short, 
thick,  and  solid  mass ; 
in  the  onion  it  is  a 
platelike  disk  at  -the 
bottom  of  the  bulb ;  in  the  dandelion  and  the  first-year  plants 
of  many  other  species  it  is  a  collarlike  organ  at  the  top  of  the 
root ;  and  in  Solomon's  seal  and  iris  it  is  a  thick,  elongated, 
subterranean,  rootlike  structure.  In  every  case  its  chief  func- 
tions are  to  properly  expose  the  leaves  to  the  light  and  to 


Fig.  37.    Conns  of  the  gladiolus 

The  right-hand  figure  shows  the  leaf  bases  re 
moved.   The  corm  is  a  form  of  stem 


Fig.  38.   The  rootstock  or  rhizome  of  Solomon's  seal 
An  underground  stem.    The  dark  spots  are  branch  scars 

transport  foods  and  food  materials.  Short-stemmed  plants 
gain  illumination  by  spreading  out  their  few  leaves  close  to 
the  earth  in  rosettes ;  others  may  send  up  a  tall  column  with 
many  branches,  upon  which  multitudes  of  leaves  are  hung; 
while  between  these  extremes  are  many  different  forms. 


THE  okganizatio:n^  of  the  plant 


65 


Structure  of  the  stem.  The  stem,  like  the  root,  has  a  central 
cylinder  and  a  cortex.  When  young  it  also  has  an  epidermis, 
but  in  perennial  stems  this  soon  gives  place  to  the  outer  hark, 
which  serves  the  same  purpose.    The  central  cylinder  is  made 


Fig.  39.   Structure  of  steins 
o,  basswood,  a  dicotyledon ;  h,  coi"n,  a  monocotyledon 

up  of  many  thin-walled  cells,  called  pith  cells,  through  which 
run  strands  of  heavier  fibers  and  two  sets  of  tubes  which  form 
the  fihrovasvidar  bundles.  It  is  the  woody  tissue  of  these  fibro- 
vascular  bundles,  packed  closely  together,  that  gives  the  trunks 


Fig.  40.    A  single  dicotyle- 
don bundle.  (Much  enlarged) 

pa,  parenchyma ;  ph,  phloem  ; 

c,    cambium;     il,    duets;    to, 

wood ;  p,  pith 


Fig.  41.    A  monocotyledon 
bundle.  (Much  enlarged) 

ph,   phloem ;    d,  ducts ; 
10,  wood ;  p,  pith 


of  trees  their  great  solidity  and  strength.  Plants  that  live  but 
a  single  season  and  rise  only  a  short  distance  above  the  earth 
do  not  need  to  develop  these  bundles  so  extensively,  though 
some  are  always  necessary. 


66 


AGRONOMY 


The  way  in  which  the  bundles  are  arranged  in  stems 
makes  it  possible  to  separate  the  flowering  plants  into  two 
very  natural  groups.  In  one,  called 
the  monocotyledonous  group,  these  bun- 
dles are  scattered  throughout  the  cen- 
tral pith.  A  cornstalk  or  an  asparagus 
stem  is  a  good  example  of  this.  In 
the  other,  known  as  the  dicotyledonous 
group,  the  bundles  are  arranged  in  a 
circle.  The  sunflower  or  any  of  our 
forest  trees  illustrates  this  type.  The 
dicotyledons  are  further  distinguished 
by  the  presence  of  a  ring  of  cambium, 
which  cuts  through  each  bundle  in  the  circle  and  separates 
the  two  sets  of  tubes.  The  part  of  the  bundle  inside  the 
cambium  is  the  ^vood  and  its  tubes  are  ducts;  the  part  out- 
side the  cambium  is  bast,  or  phloem,  and  its  tubes  are  called 


Fig.  42.  Cross  section 
of  young  dicotyledon 
stem  showing  the  circle 
of  fibrovascular  bundles 


Fig.  43.  Part  of  a  cross  section  of  year- 
old  basswood  twig 

6,  bark ;  pa,  parenchyma ;  ph,  phloem ; 

c,     cambium ;     med,    medullary    rays ; 

w,  wood;  p,  pith 


Fig.  44.  Section  of  oak  wood 

showing  the  annual  rings  and 

medullary  rays 


sieve  tubes.  Water  and  food  materials  pass  upward  through  the 
ducts,  but  elaborated  food  is  transported  downward  through 
the  sieve  tubes.    The  wedges  of  pith  that  extend  outward 


THE  ORGANIZATION  OF  THE  PLANT 


67 


The  sectioned  spec- 
imen shows  the  em- 
bryo   leaves    and 
stem 


between  the  bundles  are  called  medullary  rays.  These  serve 
to  transport  foods  across  the  stem.  The  activities  of  the 
cambium  annually  add  new  layers  to  both 
the  wood  and  bast.  In  consequence  dicoty- 
ledon stems  yearly  increase  in  diameter.  In 
the  new  wood  new  ducts  are  also  formed, 
and  these  circles  of  ducts  serve  to  distinguish 
the  wood  of  one  season  from  that  of  another. 
Monocotyledons,  on  the 
other  hand,  lack  cambium 
and  commonly  do  not  in- 
crease in  diameter  after 
the  stem  once  starts  upward.  Externally 
the  two  groups  also  present  several  notice- 
able differences.  The  monocotyledons  have 
more  conspicuous  joints,  seldom  branch, 
and,  since  they  lack  a  cambium,  have  no 
bark.  Among  the  well-known  monocoty- 
ledons are  sugar  cane,  rice,  wheat,  and  all 
the  other  grains  and  grasses,  as  well  as  such 
plants  as  the  lily,  iris,  and  tulip.  Our  fruit 
and  forest  trees  and  most  of  our  garden 
plants  are  dicotyledons. 

Buds.  All  ordinary  stems  increase  in 
length  at  the  tip.  At  this  point  the  rudi- 
mentary stem  is  crowded  with  undeveloped 
leaves,  forming  what  is  known  as  a  bud.  In 
woody  plants,  in  addition  to  this  terminal 
bud,  other  growing  points  may  develop 
along  the  sides  of  the  stem,  late  in  the 
growing  season,  from  which  new  twigs  or 
flowers  arise  the  following  year.  These 
are  called  lateral  buds.  They  always  occur  at  the  joints  of  the 
stem  and  just  above  a  leaf.    Extra  buds,  called  accessory  buds, 


Fig.  46.  Naked  buds 
of  viburnum 


tion 


Fig.  47.  Twig  of  horse- 
chestnut,  more  than 
twenty  years  old,  show- 
ing the  circular  scars 
•which  mark  the  posi- 
of  former  bud  scales.  (Re- 
duced about  one  half) 


Fig.  48.  The  two  types  of  bud  ar- 
rangement, opposite  and  alternate 
68 


THE  ORGANIZATION  OF  THE  PLANT 


69 


Fig.  49.   Accessory  buds 
of  box  elder  (Acer) 


are  often  found  with  the  lateral  buds. 
These  usually  produce  flowers.  When 
growing  pomts  originate  elsewhere,  as 
on  injured  roots  and  stems,  they  are 
called  adventitious  buds.  As  the  end 
of  the  growing  season  approaches,  the 
stem  ceases  to  elongate,  and  the  buds 
prepare  for  winter 
by  developing  va- 
rious devices  in- 
tended to  protect 
them  from  the  ef- 
fects of  the  cold. 
Bud  scales,  formed 


from  the  outer  layers  of  leaflike  parts, 

are    usually    developed,    though    some 

buds  pass  the 
winter  with- 
out them.  In 
many  species 
the  buds  are 
further  pro- 
tected by  coats 
of  hair  within 
the   scales    or 

by  a  kind  of  varnish  on  the  outer 
parts.  Others  are  almost  covered 
by  the  bark  of  the  twig  during  win- 
ter. Buds  which  are  not  protected 
by  bud  scales  are  called  naked  buds. 
On  the  return  of  spring  the  bud 
scales  that  are  too  hard  to  function 

as  leaves  are  cast  off,  the  stem  begins  to  lengthen  again,  and 

the  rest  of  the  bud  scales  develop  into  leaves.    The  lateral 


Fig.  50.  Accessory  buds 

of  the  butternut 

(Juglans) 


Fig.  51.     Accessory  buds  of 

the  golden  bell  {Forsythia) 

These  are  flower  buds 


70 


AGRONOMY 


buds  may  also  grow  into  twigs  or  flowers,  but  many  of  them 
usually  fail  to  develop.  They  may  remain  alive,  however,  but 
continue  in  a  resting  condition,  length- 
ening just  enough  each  year  to  avoid 
being  covered  by  the  new  wood  and 
bark.  Such  buds  are  called  dormant 
buds  and  are  able  to  grow  out  to  form 
twigs  if  the  other  twigs  are  injured. 

The  horticulturist  often  classes  buds  as 
leaf  buds  when  they  contain  only  leaves, 
Jiotver  buds  when  they  produce  flowers 
only,  and  mixed  buds  when  they  contain 
both  leaves  and  flowers.  Flower  buds 
that  are  formed  in  autumn  are  usually  larger  and  different 
in  shape  from  leaf  buds,  and  by  these  characteristics  they 
may  be  distinguished  even  in  winter  and  the  crop  anticipated. 


-lam 


Fig.  52.   Flower  bud  of 
the  buckeye  {^sculus) 


Fig.  53.    A  leaf  of  geranium 

lam,  lamina,  or  blade ;  pet,  petiole ; 
stip,  stipules 


Fig.  54.    Morning-glory  leaf  show- 
ing arrangement  of  the  veins 


Leaves.  The  leaf  is  essentially  an  expanded  part  of  the 
stem,  whose  chief  function  is  to  make  food  for  the  plant  from 
the  gases  in  the  air  and  the  water  and  minerals  brought  up 


THE  OEGANIZATION  OF  THE  PLANT 


71 


from  the  soil.  The  points  upon  the  stem  where  leaves  originate 
are  called  nodes,  and  the  spaces  between  are  intemodes.  Leaves 
occur  singly  or  in  pairs  at  the  nodes.  When  complete  a  leaf 
consists  of  a  flattened  green  portion,  the  blade  ;  a  stemlike  part, 
the  petiole  ;  and  where  the  petiole  joins  the  stem,  two  ear  like 


Fig.  55.    Leaf  show- 
ing pinnate  venation 

The  geranium  leaf  on 
page  53  illustrates  pal- 
mate venation 


A  '  B 

Fig.  56.    Two  forms  of  parallel  venation 

A,  lily  of  the  valley,  veined  from  base  to  apex ; 
B,  canna,  veined  from  midrib  to  margin 


or  strap-shaped  green  parts  called  stipules.  The  stipules  are 
frequently  absent,  or  they  may  take  the  form  of  spines  or  ten- 
drils. Ramifying  through  the  blade  are  strands  of  heavy  tissue 
called  veins.  These  are  really  fibrovascular  bundles  which 
serve  to  distribute  food  materials  to  the  cells  and  aid  in  keep- 
ing the  blade  expanded.    Monocotyledons  and  dicotyledons 


72 


AGRONOMY 


may  usually  be  distinguished  by  the  difference  in  the  veining 
of  the  leaves.  In  the  monocotyledons  the  main  veins  usually 
run  parallel  from  base  to  apex  or  from  midrib  to  margin,  and 
all  the  lesser  veins  are  parallel  and  joined  to  one  another  at 
the  tips.  This  is  called  parallel  venation.  In  the  dicotyle- 
dons the  venation  is  known  as  reticulated  or  netted.  Here  the 
small  veins  form  an  irregular  network  and  the  main  veins 
either    spread  out  through  the  leaf,  like  the  fingers  on  the 


Fig.  57.   Two  types  of  branched  leaves 
The  left  figure  is  pinnately  hranched ;  the  right,  palmately  hranched 

hand,  in  the  form  known  as  palmate  venation,  or  they  branch 
out  from  the  midrib,  forming  the  pinnate  venation  to  be  seen 
in  the  elm,  dandelion,  and  others.  There  are  also  two  types  of 
branched  leaves,  the  palmately  and  the  pinnately  branched, 
corresponding  to  the  two  types  of  venation  in  dicotyledons. 

Internal  structure  of  the  leaf.  Although  the  leaf  blade  is  so 
thin,  it  consists  of  several  layers  of  cells  which  show  consider- 
able differentiation  in  structure.  In  a  cross  section  there  may 
be  distinguished  an  upper  and  lower  layer  of  clear  cells,  form- 
ing the  epidermis,  between  which  are  the  layers  of  green  cells 


THE  ORGANIZATION  OF  THE  PLANT 


73 


that  give  color  to  the  leaf.   The  cells  in  the  layer  nearest  the 
upper  epidermis  are  closely  jomed  together  and  are  more  or 

JL 


Fig.  58.    Ej)idermal  cells  and  stoinata  from  the  leaf  of  the  ainaryllis,  a 
monocotyledon.    (Much  enlarged) 

less  elongated  at  right  angles  to  the  surface  of  the  leaf,  form- 
ing the  palisade  tissue.  Below  this  layer  the  cells  are  more 
loosely  joined  to  form  the  spongy  parenehyma.    The  openings 


--■int 
-sto 

Fig.  59.    Section  through 
the  leaf  of  the  beech 

ep,  epidermis;  pal,  palisade 
tissue ;     sp,    spongy    paren- 
chyma ;      hit,     intercellular 
spaces ;  sto,  stoniata 


Fig.  60.    Section  through  the  leaf 
of  the  rubber  plant 

cri,  cuticle;   ep,  epidermis;   lo,  water- 
storage  tissue ;  pal,  palisade  tissue ;  up, 
spongy  parenchyma ;  int,  intercellular 
spaces;  sto,  stomata 


between  these  cells  are  known  as  intercellular  spaces.  The 
epidermal  cells  are  nearly  air  and  water  proof,  and  to  facilitate 
the  exchange  of  gases  and  water  between  the  interior  of  the 


74  AGRONOMY 

leaf  and  the  outer  air,  therefore,  the  epidermis  contains  great 
multitudes  of  tiny  openings  called  stomata  (singular,  stoma), 
which   connect  with   the   mtercellular  spaces.     Each  stoma 


Fig.  61.   Epidermal  celLs  and  stomata  from  the  leaf  of  the  begonia,  a 
dicotyledon.    (Much  enlarged) 

is  provided  with  a  pair  of  guard  cells  roughly  semicircular 
in  shape,  which  can,  upon  occasion,  enlarge  or  diminish  the 
size  of  the  opening.    The  stomata  are  exceedingly  minute. 


THE  ORGANIZATION  OF  THE  PLANT 


75 


but  they  make  up  iu  number  what  they  lack  in  size.  There 
may  be  several  million  in  the  epidermis  on  the  underside  of  a 
single  ordinary  leaf.  The  stomata  have  been  estimated  to  oc- 
cupy nearly  one  twentieth  of  the  area  of  the  leaf.  It  is  a  curi- 
ous fact  that  gases  can  enter  the  leaf  through  these  minute 
openings  more  rapidly  than  they  can  pass  through  a  single 
opening  equal  in  area  to  all  the  stomata. 

Formation  of  plant  food.  Food  is  formed  only  in  the  green 
cells  of  the  plant.  This  is  because  the  energy  necessary  for 
combining  the  food  materials  is  derived  from  the  sunlight  by 

the  green  coloring  matter  called 
chlorophyll.  In  the  cell  this  color 
is  found  in  small  bodies  known 
as  chloroplasts.  The  chloroplasts 
really  form  the  food,  though  they 
are  helpless  without  chlorophyll. 
The  first  food  product  formed  is 
usually  grape  sugar,  represented 
by  the  formula  CgH^.^Og,  but  this 
is  soon  turned  to  starch,  a  more  stable  form  of  plant  food,  with 
the  formula  CgHj^O^.  Plants  of  the  iris,  lily,  and  amaryllis 
families  rarely  form  starch.  In  such 
plants  oil  formed  from  the  same  three 
chemical  elements  may  be  the  first  visi- 
ble product  of  photosynthesis.  Starch, 
wood,  and  several  other  substances 
contain  the  same  proportion  of  carbon, 
hydrogen,  and  oxygen,  and  the  differ- 
ence between  them  is  accounted  for  by 
assuming  a  different  multiple  of  the 
formula  for  each.  The  hydrogen  and 
oxygen  in  the  combination  are  derived  from  the  soil  water, 
and  the  carbon  comes  from  the  carbon  dioxide  in  the  air.  The 
latter  goes  into  the  leaf  through  the  stomata,  and,  spreading 


Fig 


62.    Cells  of  a  moss  with 
chloroplasts 


Fig.  63.    Stai'ch  grains  in 
the  cells  of  a  potato 


76 


AGRONOMY 


\ 


•^.v 


through  the  intercellular  spaces,  mixes  with  the  moisture  in 
the  cell  walls  and  thus  enters  the  cells.  Here  it  is  combined 
into  food  and  the  excess  oxygen  given  off.  The  whole  process 
is  known  as,  photosynthesis.  It  is  popularly  supposed  that  photo- 
synthesis in  plants  is  the  equivalent  of  respiration  in  animals, 
but  this  is  an  error.  Plants  also  respire,  exactly  as  animals  do, 
taking  in  oxygen  and  givmg  off  carbon  dioxide,  but,  unlike 
animals,  they  have  the  additional  process  of  photosynthesis, 
m  which   carbon  dioxide  is   taken  in   and  oxygen  released. 

The  two  processes 
differ  also  in  other 
respects.  Respiration 
occurs  in  every  living 
cell,  in  roots  as  well  as 
in  stems  and  leaves, 
and  goes  on  continu- 
ally, while  photosyn- 
thesis goes  on  only 
in  the  green  cells  in 
sunliglit. 

The  grape  sugar 
formed  in  the  leaves 
is,  as  we  have  noted, 
almost  immediately  turned  to  starch.  Later,  especially  at 
night,  this  food  is  distributed  through  the  plant,  by  way  of  the 
sieve  tubes,  to  be  used  in  the  formation  of  new  tissues,  or  it  is 
stored  in  stems,  roots,  and  other  organs  until  needed.  Starch, 
however,  cannot  pass  through  the  cell  walls,  and  before  it  can 
be  moved  it  must  be  turned  back  to  grape  sugar  agam.  This 
is  accomplished  by  means  of  vegetable  ferments  called  enzymes^ 
and  the  process  is  called  digestion.  A  green  and  starchy 
banana  or  pear  laid  aside  for  a  time  will  become  sweet  by  the 
same  process.  The  underground  parts  of  the  plant  are  favor- 
ite places  for  the  storage  of  food.    Here  the  grape  sugar  is 


m 


Fig.  64.    Cells  of  the  carrot  with  crystals  of 
carotin,  which  give  the  root  its  orange  color 


THE  ORGANIZATION  OF  THE  PLANT  77 

again  turned  to  starch  by  tlie  leucoplasts  or  ami/loplasts,  small 
bodies  allied  to  the  chloroplasts.  The  leucoplasts  and  starch 
grains  may  be  easily  seen  in  young  shoots  of  the  canna. 

Transpiration.  Another  important  service  performed  for 
the  plants  by  the  leaves  is  the  transpiration  of  water.  The 
transpiration  stream,  passing  off  through  the  stomata,  not  only 
keeps  the  cell  sap  denser  than  the  soil  water,  thus  providing 
for  a  continuous  inflow  of  food  materials  in  solution,  but  the 
mere  evaporation  of  so  much  moisture  enables  the  plant  to 


n 


Fig.  G5.    Cells  from  a  dahlia  root,  showing  crystals  of  iuuliii,  a  substance 

allied  to  starch 

keep  cool  in  the  midst  of  the  downpour  of  heat  on  a  summer 
day.  At  the  end  of  the  growing  season  most  of  our  broad- 
leaved  plants  prepare  for  the  approaching  winter  by  casting 
their  leaves.  By  so  doing  they  avoid  transpiration  in  winter 
when  most  of  the  moisture  in  the  soil  is  locked  up  by  the 
frost.  But  even  in  milder  climates  the  leaves  are  eventually 
thrown  off.  In  regions  of  summer  drought  they  may  all  be 
cast  at  once ;  otherwise  the  individual  leaves  fall  one  by  one, 
and  the  tree  always  has  a  crown  of  verdure.  One  reason  for 
the  casting  of  the  leaves  is  that  after  a  season  of  food  making 
a  considerable  amount  of  useless  mineral  matter  has  accumu- 
lated in  the  leaf,  which  impairs  its  usefulness.    The  ashes  from 


78 


AGRONOMY 


a  bushel  of  leaves  picked  from  a  tree  in  autumn  are  noticeably 
heavier  than  the  ashes  from  a  bushel  of  leaves  picked  from 
the  same  tree  in  spring.    The  growth  of  the  stem  and  the 


Fig.  66.   Cells  from  the  rind  of  au  orange,  showing  the  colored  chromoplasts 


production  of  new  leaves  which  shade  the  older  ones  make 
it  desirable  to  cut  off  the  latter  after  a  time.  The  fall  of  the 
leaf  is  caused  by  a  layer  of  brittle  cells  which  the  plant  con- 
structs across  the  petiole.  When  the 
parts  are  cast  off,  a  smooth  scar  is 
left,  over  which  a  thin  cover  of  bark 
is  deposited.  Great  numbers  of  flow- 
ers and  embryo  fruits  are  cut  off 
by  the  plants  in  the  same  way,  and 
many  woody  species  also  cut  off  some 
of  their  twigs.  The  latter  are  usually 
the  young  twigs  of  the  season  and  of 
the  same  age  as  the  leaves. 

The  flower.  When  the  season  for 
reproduction  arrives  the  flowers  appear.  These  may  be  re- 
garded as  transformed  branches  designed  for  reproduction. 
The  flower  when  complete  has  four  sets  of  organs,  called 


Sep 


Fig.  07.    Typical  flower  of 
the  houseleek 

pet,  petals;  sta,  stamens;  car, 
carpels ;  sep,  sepals 


THE  ORGANIZATION  OF  THE  PLANT 


79 


Fig.  68.    A  typical   mono- 
cotyledon flower 


respectively  the  sepals,  petals,  stamens,  and  carpels.  On  the 
outside  are  the  green  and  leaf  like  sepals  ;  next  within  are  the 
colored  and  more  delicate  petals;  then  come  one  or  more 
circles  of  threadlike  organs  with  knobbed  ends,  the  stamens ; 

and  last,  occupying  the  center  of  the 
flower,  are  one  or  more  bottle-shaped 
or  club-shaped  carpels.  Taken  collec- 
tively, the  sepals  form  the  calyx  and 
the  petals  the  corolla.  The  carpels 
when  united  form  the  pistil,  though 
often  the  carpels  themselves  are  called 
pistils.  The  base  of  the  pistil  is  the 
ovary  and  withm  it  are  the  ovules,  des- 
tined to  ripen  mto  seeds.  In  order 
that  fertile  seeds  be  produced,  however,  it  is  necessary  that 
the  flower  be  pollinated,  that  is,  that  the  tiny  grains  of  pollen 
formed  in  the  knobs,  or  anthers,  of  the  stamen  fall  upon  the 
stiyma  at  the  apex  of  the  pistil.  In  this  position  each  grain 
puts  out  a  pollen  tuhe  which  grows  down  through  the  sub- 
stance of  the  pistil  until  it  meets  and  enters  an  ovule,  after 
which  fertilization,  or  the  union  of  an 
egg  and  sperm,  is  accomplished.  Each 
flower,  therefore,  must  receive  at  least 
as  many  pollen  grains  as  it  ripens 
seeds,  and  it  usually  receives  many 
more,  for  some  fail  to  reach  the  stigma 
and  are  therefore  wasted.  The  end  of 
the  st-em,  from  which  the  floral  parts 
rise,  is  called  the  receptacle.  When  the 
other  sets  of  organs  in  the  flower  ap- 
pear to  spring  from  the  base  of  the  ovary,  the  flower  is  said  to 
be  hypogynous.  Sometimes  the  receptacle  grows  up  about  the 
ovary  in  such  a  way  that  the  floral  parts  seem  to  grow  from 
the  top  of  the  ovary.    In  such  cases  the  flower  is  epigynous. 


Fig.  69.    A  typical  dicoty- 
ledon flower 


80 


AGRONOMY 


Pollination.  Stamens  and  carpels  are  the  only  organs  in 
the  flower  that  are  necessary  to  the  production  of  seeds,  and 
for  this  reason  are  often  distinguished  as  the  essential  organs. 
A  considerable  number  of  plants,  of  which  the  willow  and 
Cottonwood    are    examples,   have    only  these   two   kinds   of 

organs,  showing  very 
clearly  that  the  others 
are  not  necessary.  In 
some  species  the  sta- 
mens and  pistils  are 
in  separate  flowers,  as 
in  the  pumpkin  and 
cucumber;  in  others 
they  may  be  on  sep- 
arate plants,  as  in  the 
willow.  Even  when 
both  sets  are  found  in 
the  same  flower,  as  in 
the  lily  and  most  of 
our  common  plants, 
they  are  usually  sepa- 
rated from  each  other 
by  a  distance  too  great 
to  be  bridged  with- 
out the  aid  of  the 
wind,   birds,  insects, 

A    plant    in  which    the    monocotyledon    number     and  other  affcncics.   Of 
(three)   is  especially  prominent 

these,  the  two  most 
important  are  undoubtedly  wind  and  insects.  Wind-pollinated 
flowers  are  generally  inconspicuous,  lacking  sepals  and  petals 
and  producing  neither  perfume,  pollen,  nor  nectar,  since  the 
wind  will  work  without  pay ;  but  flowers  that  depend  upon 
insects  and  birds  for  pollination  must  provide  a  reward  in 
the  form  of  nectar  or  extra  pollen,  and  must  advertise  it  by 


Fig.  70.    Trillium 


THE  ORGANIZATION  OF  THE  PLANT 


81 


fr 


Fig.  71.   A  group  of  wind-pollinated  flowers 

Those  on  the  loft  are  staminate ;  those  on  the  right  are  of  two  kinds,  the  easily 
recognized  staminate  and  the  small  starlike  jjistillate  near  the  tijjs  of  the  branches 

perfume  and  brightly  colored  petals  or  sepals.  These  latter 
organs  may  also  be  of  service  to  insect-pollinated  flowers  by 
being  so  arranged   that  visitors  cannot  remove   the  nectar 


82 


AGRONOMY 


without  being  dusted  with  pollen  and  at  the  same  time  brush- 
ing off  upon  the  pistil  the  pollen  brought  from  other  flowers. 
Many  insect-pollinated  flowers,  in  order  to  better  direct  the 
attention  of  insects  to  the  nectar,  have  various  colored  lines 
and  dots,  called  nectar  guides,  on  the  petals  and  sepals.  In 
addition,  the  petals  and  sepals  may  protect  the  nectar  from 
being  dried  up  by  the  sun  or  diluted  by  rain  and  dew.  In 
some  flowers  tlie  stamens  and  pistils  are  so  arranged  that 
pollination  may  be  effected  by  pollen 
from  their  own  stamens.  This  is  called 
self  or  close  pollination.  Usually,  liow- 
ever,  the  stigma  and  stamens  ripen  at 
different  times,  or  are  so  placed  that 
pollen  from  another  flower  is  required 
in  order  to  produce  seeds.  When  this 
occurs  the  process  is  called  cross  polli- 
nation. All  the  highly  specialized  flow- 
ers are  adapted  for  cross  pollination, 
and  this  arrangement  has  been  found 
to  produce  more  vigorous  and  versatile 
offspring.  Wind-pollinated  flowers  have 
to  produce  a  great  abundance  of  dry, 
powdery  pollen  grains  to  insure  that, 
when  these  are  intrusted  to  currents  of 
air,  enough  will  find  the  waiting  pistils  to  render  their  ovules 
fertile.  Insect-pollinated  flowers,  on  the  contrary,  having 
adopted  a  more  certain  method  of  transfer,  do  not  have  to 
produce  so  much  pollen.  In  some  species  the  flower  contams 
only  one  or  two  anthers,  and  yet  it  finds  this  number  sufficient 
for  its  needs. 

In  adapting  themselves  to  insects  and  other  agencies  for  the 
transfer  of  pollen,  flowers  have  become  more  varied  than  any 
other  organ  of  the  plant.  Running  through  all  their  variations, 
however,  a  general  plan  of  the  flower  may  be  discerned.    In 


Fig.  72.  Flower  of  the 
nasturtium  {Tropaeolum), 
with  two  large  nectar 
guides  and  three  "  false  " 
nectar  guides 

False    nectar    guides    are 

supposed  to  discourage  the 

visits  of  small  insects 


THE  ORGANIZATION  OF  THE  PLANT  83 

the  flowers  of  monocotyledons  there  are  normally  three  parts 
in  each  cu-cle,  or  whorl,  or  if  there  are  more  than  this,  the  num- 
ber is  some  multiple  of  three.  The  iris  has  three  sepals,  three 
petals,  three  stamens,         y^^*s^  -^  ^^  ^,,^»,^ 

and  a  pistil  composed  ,(^I^  /Fffi^v       {^,^\ 

ottljree  carpel.;  the  ^^  (^®.)       1^®^> 

Illy  has  three  sepals,  ^-^^^-^  >^^^                "^w^ 

three  petals,   six   Sta-  Fig.  73.  Plans  of  three  typical  flowers 

mens      and     a    three-      '^'^^  ^^^^  *  monocotyledon,  the  other  two  repre- 
,     ,  •   ,  •!         rf-11  senting  four-parted  and  five-parted  dicotyledons 

parted     pistu.      1  he 

flowers  of  dicotyledons  are  usually  distinguished  from  those 
of  monocotyledons  by  having  four  or  five  parts  in  each  circle, 
though  they  often  exhibit  a  much  wider  range  of  variation. 

The  fruit.  The  fruit  results  from  the  ripening  of  the  pistil, 
or  carpels,  often  in  conjunction  with  other  parts  of  the  flower. 
Its  development  is  one  of  the  results  of  pollination.  Flowers 
that  fail  to  secure  pollination  are  usually  cut  off  and  fall  from 
the  plant  soon  after  blooming.  There  are  many  exceptions  to 
this  rule,  however.  All  seedless  fruits,  among  which  may  be 
mentioned  navel  oranges,  seedless  grapes,  bananas,  the  currant 
of  commerce,  pineapples,  and  seedless  or  coreless  apples  and 
pears,  nuist  of  course  be  produced  without  pollination.  The 
secondary  effects  of  pollination  and  the  resultant  fertilization 
are  often  far-reaching,  and  may  extend  not  only  to  the  ovary, 
or  carpel,  but  to  the  receptacle  and  other  parts  as  well.  Fruits 
that  develop  as  the  result  of  incomplete  pollination  often  lack 
the  flavor  of  the  seeded  forms,  and  by  their  incomplete  develop- 
ment indicate  the  fact  that  they  have  failed  to  receive  sufficient 
pollen.  In  a  majority  of  fruits  the  pistil  alone  is  represented, 
as  in  peas,  beans,  plums,  and  tomatoes.  In  the  apple,  pear,  and 
similar  fruits  the  core,  only,  represents  the  pistil,  the  fleshy 
part  being  the  receptacle  that  has  grown  up  around  it. 

The  fleshy  part  of  the  strawberry  is  also  a  receptacle,  and 
all  the  seedlike  parts  upon  it  are  the  remains  of  tuiy  pistils, 


Fig.  74.   Fruits  modified  for  wind  distribution 

A,  ironwood;   B,  white  ash;  C,  ailanthus;   D,  hop  tree;   E,  box  elder; 

F,  basswood ;   G,  pine ;  H,  locust ;  /,  silver  bell ;  J,  sterculia ;  K,  black 

ash ;  L,  Norway  maple 


84 


THE  ORGANIZATION  OF  THE  PLANT 


85 


eacli  consisting  of  a  single  carpel.  In  the  blackberry  each 
small  pistil  becomes  fleshy  and  the  receptacle  serves  merely 
to  hold  them  together.  The  raspberry  is  somewhat  like  the 
blackberry,  but  when  ripe  the  pistils  separate  from  the  recep- 
tacle. A  few  fruits,  such  as  the  mulberry,  pineapple,  and 
osage  orange,  are  the 
product  of  several 
flowers  and  are  called 
compound  fruits.  In 
the  pineapple  each 
"  eye  "  represents  a 
separate  flower. 

The  object  of  the 
plant  in  producing 
flowers  and  fruits  is, 
of  course,  the  contin- 
uation of  the  species 
by  the  formation  of 
seeds.  Many  plants 
too  tender  to  en- 
dure great  cold  or 
drought  are  able  to 
form  seeds  that  can 
do  so,  and  thus  the 
life  of  the  species  is 
carried  over  the  un- 
favorable season.  In 
addition,  seeds  may 
multiply  and  distribute  the  plants  as  well.  The  fruit  is  de- 
signed to  protect  the  developing  seeds  and  to  aid  in  distribut- 
ing them  when  mature.  In  some  the  fruit  becomes  sweet 
and  juicy,  to  attract  birds  and  mammals ;  in  others  it  forms 
winglike  sails,  by  means  of  which  the  seeds  are  carried  long 
distances  by  the  wind ;  in  still  others  it  develops  hooks  that 


Fig.  75.   Seeds  modified  for  wind  distribution 

A,  buttonwood;    B,  cat-tail;    C,  trumpet  creeper; 
1),  catalpa ;   E,  dandelion ;   F,  clematis ;    <l,  olean- 
der; //,  actiuomeris ;  /.anemone;  ./,  milkweed 


86 


AGRONOMY 


-h  —  tCS 


Fig.  76.    External  view  of 
lima  bean 

mic,  micropyle ;    hll,  hilum ; 
tes,  testa 


catcli  into  the  clothing  of  man  and  the  other  animals ;  while 
not  a  few  shoot  their  seeds  for  some  distance   or  in  other 

ways  provide  for  their  dispersal. 

The  seed.  The  seed  consists  of  an 
outer  covering,  called  the  testa,  within 
which  is  a  young  plant,  or  embryo.  The 
testa  is  marked  externally  by  a  scar, 
the  Idliim,  where  the  seed  was  attached 
to  the  parent  plant.  Near  the  hilum  is 
a  tiny  opening  through  the  testa  called 
the  micropyle.  The  embryo  always 
consists  of  a  stemlike  part,  the  cauli- 
cle,  to  which  are  attached  one  or  two  seed  leaves,  or  cotyledons. 
In  most  cases  a  tuft  of  very  rudi- 
mentary leaves,  a  bud  in  fact,  is  found 
at  one  end  of  the  caulicle.  This  is 
the  plumule.  The  embryo  is  always 
provided  with  a  food  store  sufficient 
to  give  it  a  start  in  life.  In  plants 
like  the  bean  this  food  supply  may 
be  stored  in  the  young  plant  or  it 
may  be  stored  within  the  testa  but 
outside  the  embryo,  as  in  the  castor 
bean,  in  which  case  it  is  known  as  the  endosperm,  or  albumen. 
So  unvaryhig  is  the  occurrence  of  either  one 
or  two  cotyledons  in  each  kmd  of  seed  that  this 
fact  is  commonly  seized  upon  to  divide  the 
world  of  flowering  plants  into  two  groups.  The 
plants  whose  seeds  contain  only  one  cotyledon 
are  called  monocotyledotis,  and  those  whose  seeds 
contain  two  are  called  dicotyledons.  The  differ- 
ences between  the  groups,  as  we  have  seen,  are 
not  confined  to  the  cotyledons  alone,  but  are  manifested  in 
all  the  conspicuous  parts  of  the  plant. 


Fig.  77.  Embryo  of  lima  bean 

plu,    plumule;     can,    caulicle; 
cot,  cotyledon ;  tes,  testa 


Fig.  78.  Seed 
of  the  castor 
bean,  showing 
the  projecting 
caruncle 


THE  ORGANIZATION  OF  THE  PLANT  87 

Life  cycle  of  plants.  The  life  cycle  of  some  plants  is  com- 
pleted ill  a  single  season.  They  spring  up,  flower,  produce 
.^„„  their  seeds,  and  disappear  within  the  interval 
■plu  of  a  few  weeks  or  months.  On  the  other 
"^^'^  hand,  some  of  the  lofty  trees  that  still  inhabit 
'  the  earth  have  been  growing  for  many  hun- 

FiG.  79.  Seed  dreds  or  even  thousands  of  years.  As  regards 
of  honey  locust  their  length  of  life,  however,  plants  may  be 
caw,cauiicie;;)/M,  (jjvided  into  three  groups  —  annuals,  biennials, 

plumule;  co^.eoty-  .  . 

ledon ;  en<7,  eiuio-  and  perennials.     An   annual   is    a   plant    that 

sperm,     es,    es  a    QQjj^plg^gg   j^g  J^fg  cycle  within         /^f^'B^- ■ -coi 

a  year.  This  may  occur  during  a  single  grow-      (  \\4|-«.-catt 
ing  season,  as  in  the  radish,  when  it  is  called       \^^^..end 
a  summer  annual ;  or  the  plant  may  spring  up     j-j^.  go.   Embryo 
in  autumn,  live  through  the  winter,  and  fruit       of  four-o'clock 
in  the  spring,  as  in  some  varieties  of  wheat,       ^J^J^^  ''^caiiSe  • 
thus  becoming  a  tvinter  annual.    Several  of       end,  endosperm 
the  common  summer  annuals  of  our  gardens  may  be  treated  as 
winter  annuals.    Lettuce  and  spinach  are  sometimes  grown  in 
this  way.  It  is  clear  from  the  behavior  of  these  plants  that  they 
do  not  die  from  the  cold  but  are  killed  by  fruiting.   Biennials 

f  differ  from  annuals  in 
end /          \^M     that  they  require  two 
cot ^M|r-y^     growing    seasons    to 
^»    /  J     complete  the  round  of 
^          I      their  existence.    The 
V      "^^      first  year  they  store  up 
N^^^^,  J^        much  food,  which  they 
v/  use  the  second  year  in 
Fig.  81.  Grain  of  corn  producing  seeds.  Car- 

The  fruit  and  seed  of  a  monocotyledon,  end,  endo-  rotS,  salsify,  and  bects 
sperm  ;  cot,  cotyledon ;  j^ln,  plumule ;  cau,  caulicle  . 

are  biennials.  In  re- 
gions with  a  long  growing  season  the  line  dividing  an- 
nuals from  biennials  breaks  down  more  or  less  completely. 


88 


AGRONOMY 


Fig.  82.   The  showy  lady 's-slipper  (Cj/pnpedtum  specfaWte) 
A  type  of  the  highest  monocotyledons 

Perennials  are  plants  that  live  more  than  two  years.  They 
are  not  killed  by  fruiting,  though  this  makes  heavy  drafts 
upon  their  vitality.    Like  biennials,  most  perennials  store  up 


THE  ORGANIZATION  OF  THE  PLANT  89 

more  or  less  food  in  summer,  which  is  expended  in  growth 
during  the  following  spring.  The  rhubarb  and  asparagus, 
among  garden  vegetables,  and  the  lily  and  iris,  among  decora- 
tive plants,  are  good  examples  of  this.  Most  of  the  asparagus 
crop  is  produced  from  food  made  by  the  plant  the  preceding 
year.  There  are  two  classes  of  perennials.  In  the  herbaceous 
perennials  the  stems  die  down  to  the  ground  in  winter.  Lilies, 
peonies,  asparagus,  and  rhubarb  are  examples  of  this  class. 
The  woody  perennials  comprise  our  trees,  shrubs,  vines,  and 
other  forms  that  put  up  stems,  which  continue  to  live  for  a 
succession  of  years.  Trees  have  a  single  trunk  and  usually 
attain  heights  of  more  than  twenty  feet.  Shrubs  have  several 
stems  and  are  less  than  twenty  feet  high.  Bushes  resemble 
shrubs,  though  they  are  somewhat  smaller,  usually  being  no 
taller  than  a  man.  Vines  have  stems  too  weak  to  stand  alone 
and  consequently  must  be  supported  by  stronger  plants.  They 
may  be  root  climbers  like  the  poison  ivy,  twiners  like  the  bitter- 
sweet, true  climbers  like  the  grape  and  woodbine,  or  scramblers 
like  the  climbing  rose. 

The  rest  period  of  plants.  In  perennial  species,  after  a 
season  of  growth,  the  vegetative  processes  gradually  cease, 
buds  are  formed,  the  leaves  are  thrown  off,  the  wood  cells 
thicken,  and  the  protoplasm,  excludmg  much  of  its  moisture, 
goes  into  a  resting  condition.  It  is  likely  that  this  season  of 
dormancy  was  originally  m  response  to  a  change  in  the  season, 
for  in  northern  regions  it  occurs  at  the  beginnmg  of  winter 
and  in  the  tropics  at  the  beginning  of  the  dry  season.  A 
period  of  rest,  however,  seems  natural  to  most  plants.  Many 
seeds  refuse  to  grow  if  planted  as  soon  as  ripe ;  the  spring 
flowering  plants  will  not  respond  ta  warmth  when  brought 
into  the  house  in  early  winter ;  and  potatoes,  onions,  parsnips, 
and  the  like,  stored  in  cellars,  do  not  begin  to  sprout  until 
the  approach  of  spring.  The  hyacinth,  narcissus,  crocus,  and 
tulip,  after  flowering  in  the  open  gi-ound,  ripen  theii"  foliage 


90  AGRONOMY 

and  remain  dormant  during  the  summer,  but  in  autumn  begin 
to  grow  again,  making  more  or  less  root  growth  all  winter. 
The  white,  or  Madonna,  lily  rests  for  a  time  in  summer  and 
makes  new  growth  m  autumn.  Possibly  half  the  species  of 
crocus  produce  their  flowers  in  autumn,  and  the  witch-hazel  is 
a  well-known  slirub  with  the  same  habit.  Greenhouse  plants, 
coming  as  they  do  from  a  region  in  which  the  season  of  rest 
is  the  dry  season,  are  benefited  by  withholdmg  water  after 
the  season  for  growth  is  over.  Calla  lilies  and  other  bulbous 
plants  are  often  allowed  to  become  entirely  dry  after  flowering. 
Our  own  plants  seem  to  be  adjusted  to  a  season  of  cold  for 
the  rest  period,  though  in  many  cases  an  exposure  to  dryness 
is  as  effective.  In  cold  climates  hardiness  is  often  a  matter 
of  complete  dormancy. 

Genera,  species,  and  varieties.  Although  each  kind  of  plant 
has  adopted  the  form  most  suited  to  its  position  in  life,  and 
in  consequence  has  become  different  from  all  others,  this  has 
not  resulted  in  a  multitude  of  disconnected  forms.  Strong 
lines  of  resemblance  run  through  the  different  groups,  and, 
mterwoven  through  the  vegetable  kingdom,  bhid  it  into  one 
related  whole.  As  a  general  thing,  the  more  decided  the  re- 
semblance between  different  forms,  the  closer  the  relationship. 
There  are  certain  types  of  leaf  and  flower  on  which  nature 
has  rung  a  thousand  changes,  producing  plant  after  plant 
essentially  alike  though  ever  varied.  The  casual  observer 
dqes  not  fail  to  note  these  differences,  and  usually  recognizes 
groups  like  the  violets,  lilies,  asters,  grasses,  and  legumes  at 
sight,  though  he  may  fail  when  it  comes  to  the  lesser  distinc- 
tions that  separate  species  from  species.  The  botanist,  how- 
ever, finds  it  convenient  to  carefully  delimit  these  smaller 
divisions.  To  the  unit  of  his  classification  he  gives  the  name 
of  species  and  defines  it  as  a  group  of  like  individuals.  All 
the  plants  of  white  clover  or  of  field  corn  form  a  species. 
Genera  (singular,  yenu*^  are  groups  of  related  species.    Red 


THE  ORGANIZATION  OF  THE  PLANT  91 

clover,  white  clover,  yellow  clover,  and  many  other  clover 
species  belong  to  the  clover  genus,  and  all  have  a  common 
resemblance  in  leaf,  flower,  and  fruit.  Going  beyond  the 
clovers,  however,  one  finds  many  other  plants  whose  general 
appearance  suggests  a  relationship  to  them.  Among  these  are 
beans,  peas,  alfalfa,  vetch,  locust,  cowpeas,  and  soy  beans. 
These  differ  enough  to  be  put  in  different  genera,  but  all  are 
included  with  the  clovers  in  a  larger  group  called  2k  family, 
which  holds  the  same  relation  to  genera  as  the  genera  them- 
selves hold  to  species.  The  family  to  which  the  clovers  and 
their  allies  belong  is  the  Leguminosre,  or  legume  family.  There 
are  more  than  two  hundred  of  these  families,  each  composed 
of  many  genera  and  species.  In  a  similar  way  families  are 
grouped  in  orders.  The  legumes  are  placed  with  the  rose- 
worts  and  various  others  in  the  order  Rosales. 

The  species  themselves,  though  called  groups  of  like  indi- 
viduals, constantly  exhibit  minor  differences  that  may  be 
brought  out  by  selection  or  by  modifying  the  surroundings 
of  the  plant.  The  radish  is  a  species,  but  cultivation  has  made 
■many  forms  of  it.  Such  forms  the  gardener  calls  varieties,  but 
the  botanist  calls  them  elementary  species.  The  cultivated 
cabbage  has  produced  several  striking  elementary  species  or 
varieties,  among  which  are  included  kale,  collards,  cauliflower, 
Brussels  sprouts,  and  kohl-rabi. 

Scientific  names.  Scientists  have  given  each  species  of  ani- 
mal and  plant  a  scientific  name  to  facilitate  handling  it  in 
literature,  correspondence,  and  conversation.  These  names 
have  usually  been  taken  from  the  Latin  or  Greek  and  have 
the  merit  of  being  the  same  the  world  over — an  obvious  ad- 
vantage when  the  common  or  popular  name  may  change  from 
one  locality  to  another  and  is  rarely  the  same  in  the  tongues 
of  different  nations.  In  speaking  to  our  neighbors  we  may 
use  the  common  name  only,  but  in  dealing  with  strangers  it 
may  often  be  necessary  to  use  the  scientific  name  to  avoid 


92  AGRONOMY 

being  misunderstood.  Each  species  has  a  specific  name  con- 
sisting of  a  single  word,  which  is  applied  to  it  much  as  the 
given  names  of  people  are  applied  to  them.  Such  specific 
names  as  alha^  "white  ";  rubra,  "red  ";  and  wMZ</are," common," 
are  frequently  used.  The  generic  name,  always  written  before 
the  specific,  shows  to  what  larger  group  a  species  belongs. 
Thus  the  crimson  clover  is  TnfoUum  inearnatum.  The  red 
clover  is  also  a  species  of  Trifolium  called  Trifolium  pratense. 
Only  one  species  in  each  genus  can  have  the  same  specific 
name,  though  this  may  be  used  again  and  again  in  other 
genera.  Alba  is  a  common  specific  name  for  white-flowered 
species  in  many  genera.  The  generic  name,  however,  can  be 
used  for  but  one  group  of  plants.  There  is  but  one  genus 
Trifolium  m  all  the  world.  In  naming  lesser  divisions  of  a 
species  it  is  customary  to  give  them  varietal  names  taken 
from  the  Latin  or  Greek,  though  in  many  cases  such  plants 
are  named  after  prominent  persons,  gardeners,  and  the  like. 

PRACTICAL  EXERCISES 

1.  Strip  off  a  piece  of  epidermis  from  one  of  the  scales  of  an  onion 
bulb,  mount,  and  examine  with  the  microscoj)e.  Find  and  label  all  parts 
of  the  cell  mentioned  on  page  57.  In  the  cells  of  ditch  moss  or  the  hairs 
from  the  flowers  of  gloxinia  or  tradescantia,  note  the  circulation  of  the 
protoplasm. 

2.  Make  thin  sections  of  a  potato  and  examine  in  the  same  way,  to 
see  starch  grains.  Apply  a  drop  of  dilute  iodine  solution  to  a  piece  of 
laundry  starch.  Note  the  color.  Test  the  mount  of  potato  in  the  same 
way. 

3.  Mount  a  leaf  of  the  ditch  moss  (^Elodea)  or  a  leaf  from  any  of 
the  broad-leaved  true  mosses  and  note  the  chloroplasts. 

4.  Mount  thin  sections  of  the  carrot  or  orange  peel  and  examine 
the  chromoplasts.  Make  a  similar  mount  of  the  epidermis  from  the 
underside  of  a  nasturtium  petal. 

5.  Soak  seeds  of  radish  or  mustard  for  a  short  time  and  throw  them 
against  the  inside  of  a  clean  moist  flowerj)ot  to  which  they  will  stick. 
Invert  the  flowerpot  over  a  shallow  dish  of  water  for  a  few  days  and 


THE  ORGANIZATION  OF  THE  PLANT  93 

an  abundance  of  root  hairs  will  be  produced  by  the  germinating  seeds. 
Examine  with  the  microscope. 

6.  Make  longitudinal  and  cross  sections  of  parsnip  or  carrot  to  see 
the  regions  of  the  root.    Find,  draw,  and  label  the  parts. 

7.  Make  thin  cross  sections  of  any  young  root  and  examine  with 
the  microscope  for  the  cellular  structure. 

8.  Perform  the  experiment  with  osmosis  described  on  imge  63. 

9.  Peel  one  end  of  a  potato,  set  the  peeled  end  in  a  dish  of  water, 
make  a  hole  an  inch  or  more  deep  in  the  other  end,  and  in  this  hole  put 
some  dry  sugar.    Explain  the  moisture  that  appears  in  the  hole. 

10.  Cut  slices  of  potato  a  quarter  of  an  inch  thick  and  place  some 
in  salt  water  and  some  in  fresh  water.  Account  for  the  difference  in 
rigidity  in  the  two  sets  at  the  end  of  an  hour. 

11.  Make  cross  sections  of  cornstalk  or  asparagus  and  compare  with 
similar  sections  of  geranium,  begonia,  or  any  of  our  forest  trees.  Make 
sketches  to  show  the  differences  noted. 

12.  In  a  thin  section  of  begonia  or  geranium  stem  locate  the  pith, 
wood,  ducts,  bast,  and  cortex. 

13.  Get  a  thrifty  young  willow  twig  and  girdle  it  by  removing  a 
ring  of  bark  an  inch  wide  two  or  three  inches  from  the  lower  end. 
Stand  this  in  water  so  that  the  girdled  jiortion  is  covered.  Where  do 
roots  appear?  What  light  does  this  throw  on  the  passage  of  foods 
and  food  materials  through  the  stem  ? 

14.  On  twigs  of  lilac,  cherry,  peach,  golden  bell,  cottonwood,  or 
horse-chestnut  locate  the  flower  and  leaf  buds. 

15.  Locate  accessory  buds  in  walnut,  pipevine,  red  maple,  box  elder, 
butternut,  and  jieach. 

16.  Select  leaves  to  illustrate  parallel,  palmate,  and  pinnate  vena- 
tion.   Make  sketches  to  show  the  different  forms. 

17.  With  the  microscope  examine  the  epidermis  from  the  underside 
of  a  leaf  for  the  stomata.    Draw. 

18.  In  a  thin  cross  section  of  a  leaf  locate  the  tissues  described  on 
page  72. 

19.  Thrust  the  petiole  of  a  geranium  leaf  through  a  small  hole  in  a 
piece  of  cardboard  and  place  the  latter  so  that  the  petiole  of  the  leaf 
will  dip  into  a  glass  of  water.  Over  the  blade  of  the  leaf  invert  a  drink- 
ing glass,  which  should  rest  upon  the  cardboard.  Explain  the  presence 
of  the  moisture  that  forms  on  the  upper  glass  in  a  short  time. 


94  AGRONOMY 

20.  Select  a  representative  flower  and  locate  the  organs  named  on 
page  79. 

21.  Distinguish  the  monocotyledons  from  tlie  dicotyledons  in  as 
many  diiferent  kinds  of  flowers  as  you  can  find. 

22.  Locate  the  nectar  guides  and  nectaries,  if  any,  in  barberry, 
buttercup,  toadflax,  catalpa,  horse-chestnut,  nasturtium,  and  phlox. 

23.  Decide  whether  the  following  were  produced  by  hyjwgynous  or 
epigynous  flowers :  apple,  orange,  banana,  i)ear,  cranberry,  olive,  and 
tomato. 

24.  Make  a  collection  of  seeds  to  show  as  many  methods  of  seed 
dispersal  as  possible.    Visit  the  nearest  museum  for  other  examples. 

25.  Find  the  two  cotyledons  in  the  bean  and  the  single  one  in  the 
com.  Examine  other  seeds  to  discover  whether  they  are  monocotyledons 
or  dicotyledons.    In  which  seeds  do  you  find  endosperm  ? 

References 

Atkinson,  "  College  Botany." 
Bergen  and  Caldwell,  "Practical  Botany." 
Bergen  and  Davis,  "Principles  of  Botany." 
Campbell,  "  University  Text-Book  of  Botany." 
Clute,  "  Laboratory  Botany  for  the  High  School." 
Coulter,  Barnes,  and  Cowles,  "  Textbook  of  Botany." 
Green,  "Vegetable  Physiology." 
Stevens,  "Plant  Anatomy." 


CHAPTER  VI 

THE  ELEMENTS  NEEDED  BY  PLANTS 

Source  of  the  elements.  The  chemical  elements  indispensable 
to  plants  are  ten  in  number  ;  namely,  oxygen,  hydrogen,  nitro- 
gen, potassium,  magnesium,  calcium,  iron,  sulphur,  phosphorus, 
and  carbon.  Several  others  have  been  found  in  plants,  but 
these  have  been  proved  unnecessary  by  growing  plants  to 
maturity  in  media  in  which  these  elements  were  lacking.  Al- 
though the  ten  elements  indicated  are  all  essential,  most  of 
them  are  taken  in  very  minute  quantities.  The  small  amount 
of  ashes  left  when  wood  is  burned  represents  the  mineral 
matter  taken  up  by  the  plant  in  forming  it,  and  much  of  this 
is  likely  to  be  silicon  and  other  elements  that  are  nonessen- 
tial. Very  little  is  known  of  the  part  played  by  some  of  the 
essential  minerals  in  the  economy  of  the  plant.  Possibly  their 
presence  acts  simply  as  a  stimulant  for  various  plant  processes. 
The  only  element  taken  entirely  from  the  air  is  carbon.  Oxy- 
gen is  taken  from  the  air  for  respiration,  but  that  used  in 
making  food  is  taken  combined  with  hydi-ogen  as  soil  water. 
All  the  other  elements  are  derived  from  the  soil,  in  which  they 
exist  as  compounds  and  not  as  single  elements.  These  com- 
pounds are  usually  chlorides,  carbonates,  sulphates,  phos- 
phates, and  nitrates.  In  most  of  these  there  is  considerable 
oxygen,  the  termination  ate  in  the  names  of  the  compounds 
indicating  its  presence.  These  materials  are  dissolved  out  of 
the  soil  by  the  soil  water  and  carried  into  the  plant  by  osmosis. 

Selective  absorption.  Analysis  of  the  ash  of  plants  has  shown 
that  all  the  species  of  a  given  area  do  not  contain  the  same 
proportion  of  the  different  minerals,  though  growing  under 

95 


96  AGRONOMY 

exactly  the  same  conditions  and  absorbing  the  same  soil  water. 
Clover  when  growing  with  barley  may  take  up  five  or  six  times 
as  much  lime  as  the  barley  does,  while  the  latter  takes  up 
eighteen  times  as  much  silica  as  the  clover.  Similar  differences 
in  the  absorption  of  food  materials  are  found  m  other  plants. 
It  is  as  if  each  plant  exercised  a  conscious  selection.  Such  a 
condition,  however,  is  to  be  explamed  on  purely  physical 
grounds  by  what  is  known  as  selective  absorption.  When  minute 
quantities  of  any  mmeral  are  dissolved  in  the  soil  water,  they 
will  pass  into  the  plant  by  osmosis,  but  in  every  instance  each 
substance  in  the  water  acts  with  reference  to  similar  substances 
in  the  plant  as  if  it  were  the  only  element  concerned.  It  fol- 
lows, therefore,  that  if  the  plant  happens  to  be  using  a  certain 
substance,  the  depletion  of  the  supply  in  the  cells  will  induce 
more  of  it  to  filter  in ;  but  if  the  plant  has  no  use  for  it,  the 
density  of  the  solution  for  this  particular  substance  on  both 
sides  of.  the  cell  wall  soon  becomes  equal  and  the  osmotic 
action  with  reference  to  it  ceases.  Plants  cannot  exclude 
poisons  and  other  harmful  or  useless  substances  when  suffi- 
ciently diluted  by  the  soil  water. 

Use  of  water  to  the  plant.  In  addition  to  carrying  the  dis- 
solved minerals  into  the  plant,  water  forms  a  very  essential 
part  of  the  plant  food,  maintains  the  turgor  of  the  cells  and 
thus  keeps  the  plant  in  shape,  is  the  medium  in  which  all  the 
vital  processes  of  the  plant  go  on,  aids  in  the  transfer  of  food 
within  the  plant,  and,  finally,  by  its  evaporation,  serves  to  cool 
the  plant  and  keep  the  cell  sap  denser  than  the  soil  water. 
The  amount  of  water  transpired  by  growing  plants  is  remark- 
able. It  is  estimated  that  for  every  pound  of  dry  matter  pro- 
duced by  ordinary  crops,  from  250  to  400  pounds  of  water  is 
transpired,  while  mustard  is  said  to  require  900  pounds  of 
water  for  each  pound  of  dry  matter.  A  healthy  apple  tree  has 
been  estimated  to  transpire  35,000  pounds  of  water  during 
the  growing  season.    A  moist  spot  may  be  drained  through 


THE  ELEMENTS  NEEDED  BY  PLANTS  97 

the  simple  expedient  of  planting  such  water-lovhig  species  as 
willow  and  Cottonwood  in  the  vicinity.  A  great  part  of  the 
living  plant  is  water.  Turnips,  melons,  and  the  like  contain 
more  than  90  per  cent  of  water,  and  even  in  air-dry  plants  the 
amount  is  seldom  less  than  10  per  cent.  The  amount  of  water 
may  differ  greatly  in  different  parts  of  the  same  plant ;  thus 
the  flesh  of  the  watermelon,  peach,  plum,  and  the  like  contain 
much  more  water  than  the  seeds  or  the  vegetative  parts  of 
the  specimen. 

Root  pressure.  Most  of  the  water  given  off  by  plants  escapes 
through  the  stomata  as  water  vapor,  but  occasionally,  as  at  the 
close  of  a  warm  day  in  summer,  the  roots  may  continue  to  absorb 
more  than  the  leaves  can  evaporate  in  the  cool  air  of  evening. 
This  excess  moisture  may  appear  on  the  leaves  as  minute  glob- 
ules or  even  larger  drops  of  water.  Such  excretion  of  water 
is  called  ffuttation,  and  the  force  exerted  by  the  roots  in  send- 
ing it  upward  is  root  pressure.  In  some  plants  this  force  is  very 
great.  In  the  birch  it  is  sufficient  to  hold  up  a  column  of  water 
more  than  eighty  feet  high.  It  is  root  pressure  that  causes 
grapes  to  "  bleed "  when  trimmed  in  spring,  and  the  same 
force  makes  the  sap  run  from  wounds  in  trees.  The  drops  of 
water  to  be  seen  on  the  leaves  of  such  plants  as  nasturtium  in 
the  early  morning  are  due  to  root  pressure,  and  so  is  much  of 
what  passes  for  dew  on  grassy  areas.  Often  the  roots  of  weeds 
cut  down  by  the  hoe  will  continue  to  send  up  water  for  some 
time  and  show,  by  a  moist  sj)ot  in  the  dry  surface  soil,  where 
each  plant  stood. 

Carbon  dioxide.  The  gas,  carbon  dioxide,  though  found  in 
the  atmosphere  in  so  small  an  amount  as  three  parts  in  ten 
thousand,  is  nevertheless  the  only  source  of  the  carbon  in 
plants.  In  a  ton  of  dry  wood  at  least  a  thousand  pounds  is 
carbon,  all  of  which  has  been  derived  from  the  air.  The  carbon 
in  our  hard  and  soft  coals,  peat,  and  the  like  was  stored  up  in 
the  same  way  and  from  the  same  source  in  other  days.    This 


98  AGRONOMY 

element  is  the  characteristic  element  of  all  animal  and  plant 
life,  as  silicon  is  of  the  mineral  kingdom,  but  the  carbon 
fixed  in  any  form  of  organic  life  is  only  one  stage  in  a  constant 
cycle  of  changes.  Upon  the  death  of  the  organism  it  is  again 
united  with  oxygen  by  the  processes  of  decay  and  liberated 
as  carbon  dioxide,  only  to  be  selected  by  new  plants  and  formed 
into  starch  and  plant  tissues  again.  Though  forming  so  small 
a  proportion  of  the  air,  it  is  nevertheless  estimated  that  there 
are  3,400,000,000,000  tons  of  it  in  the  atmosphere  —  more 
than  25  tons  for  each  acre  of  soil.  In  plants  and  animals  carbon 
is  most  frequently  found  united  with  hydrogen  and  oxygen  to 
form  carbohydrates,  a  carbohydrate  being  defined  as  a  substance 
consisting  of  these  three  elements,  with  the  hydrogen  and 
oxygen  in  the  proportions  in  which  they  form  water.  Starch, 
sugar,  wood,  and  cellulose  are  all  carbohydrates. 

Nitrogen.  Four  fifths  of  the  air  is  nitrogen,  but  ordinary 
plants  cannot  use  it.  Their  supply  is  derived  almost  entirely 
from  the  nitrogen  in  the  humus  of  the  soil.  A  few  plants,  to 
be  described  later,  are  able  to  make  use  of  atmospheric  nitro- 
gen, but  the  rest  use  nitrogen  only  in  the  form  of  nitrates ; 
that  is,  nitrogen  combined  with  other  elements,  such  as  calcium, 
potassium,  magnesium,  sodium,  and  the  like.  One  of  the  chief 
uses  of  these  latter  elements  to  plants  seems  to  lie  in  their 
ability  to  combine  with  nitrogen  in  a  form  that  the  plants  can 
use.  Nitrogen  is  one  of  the  elements  most  frequently  lacking 
in  soils,  though  there  are  not  less  than  35,000  tons  in  the  air 
over  each  acre  —  worth  about  ten  million  dollars  at  present 
prices  if  it  were  only  available  for  plants.  Nitrogen  intensifies 
the  color  of  plants,  increases  the  growth  of  leaves  and  stems, 
and,  when  abundant,  may  hinder  seed  formation  by  favoring 
growth  processes.  Some  grain  crops,  when  supplied  with  plenty 
of  nitrogen,  grow  so  luxuriantly  that  the  stems  are  unable  to 
support  the  weight  of  the  plant.  Nitrogen  is  also  necessary  for 
the  formation  of  protoplasm  and  all  other  proteins. 


THE  ELEMENTS  NEEDED  BY  PLANTS     99 

Calcium  and  magnesium.  Calcium  and  magnesium,  which 
are  much  ahke,  are  most  familiar  to  us  in  limestone  and  dolo- 
mite. In  addition  to  being  useful  in  forming  compounds  with 
nitrogen  that  the  plant  can  use,  these  elements  form  unions 
with  various  acids  in  the  plant  which  would  otherwise  be 
harmful.  Calcium  is  an  important  part  of  the  chlorophyll  and 
nucleus,  and  promotes  the  hardiness  of  plants.  On  soils  con- 
taining much  calcium  or  lime,  plants  endure  drought  and  frost 
much  better  than  in  soils  in  which  it  is  lacking.  Certain  plants, 
such  as  alfalfa,  clover,  peas,  and  beans,  are  often  known  as 
lime  plants  because  they  cannot  exist  in  soils  deficient  in  this 
element.  Spinach,  beets,  lettuce,  and  many  others  cannot  grow 
without  lime.  On  the  other  hand,  many  plants  of  sandy  and 
boggy  soils  are  so  sensitive  to  lime  that  they  cannot  endure 
even  small  amounts  in  the  soil  water.  Magnesium  is  important 
in  forming  seeds,  and  its  absence  may  not  be  noticed  until 
flowers  and  fruits  fail  to  develop.  While  absolutely  essential 
to  plant  growth,  magnesium  in  the  absence  of  lime  acts  like 
a  poison.  Calcium  is  usually  more  abundant  than  magnesium 
in  leaves  and  stems,  but  in  seeds  the  ratio  is  usually  reversed. 

Potassium  and  phosphorus.  Potassium  is  supposed  to  aid  in 
the  production  and  transportation  of  the  carbohydrates  and 
to  reduce  the  acidity  of  cell  sap.  It  increases  the  turgidity  of 
the  cell  and  hastens  the  ripening  of  wood  and  fruit.  It  also 
increases  the  plant's  resistance  to  frost  and  is  reputed  to  deepen 
the  color  of  flowers  and  fruits.  Certam  plants  contain  so  much 
potassium  or  potash  that  they  are  called  potash  plants.  Phos- 
phorus is  associated  with  the  production  of  proteins,  and  its  lack 
prevents  the  development  of  seeds.  Fleshy  roots  may  also  con- 
tain much  potassium.  When  soils  are  deficient  in  this  element 
the  addition  of  sodium  is  followed  by  renewed  plant  growth. 

Sulphur  and  iron.  Sulphur  and  iron,  so  frequently  found 
together  in  nature,  are  necessary  constituents  of  protoplasm. 
Iron  is  also  essential  to  the  formation  of  chlorophyll  hi  plants. 


100  AGRONOMY 

Chlorine,  silicon,  and  others.  Small  amounts  of  chlorine, 
silicon,  sodium,  manganese,  aluminum,  and  other  minerals  are 
usually  found  in  the  ash  of  plants.  They  are  present  in  most 
soils  and,  being  dissolved  in  the  soil  water,  flow  into  the  plant 
with  it.  Silicon  is  often  abundant  in  the  older,  denser  parts 
of  plants,  and  the  flinty  exterior  of  scouring  rushes  and  grass 
stems  is  due  to  it.  The  "  shells  "  of  diatoms  and  the  stems  of 
certain  scouring  rushes  contain  so  much  silicon  or  silica  that 
the  organic  parts  may  be  burned  or  dissolved  out,  leaving  a 
perfect  skeleton  of  the  mineral.  Silica,  however,  does  not 
appear  to  be  essential  to  the  life  of  the  plant.  It  was  once 
thought  that  it  was  necessary  to  give  strength  to  the  stems  of 
grasses  and  other  plants,  but  this  is  shown  to  be  a  mistake 
by  the  fact  that  silica  is  often  many  times  more  abundant 
in  the  leaves  of  plants  than  in  their  stems.  Some  regard 
chlorine  as  essential,  since  it  is  usually  present  in  the  plant. 

PRACTICAL  EXERCISES 

1.  Take  two  geranium  leaves  and  place  one  in  fresh  water  and  the 
other  in  a  10  per  cent  salt  solution  for  half  an  hour.  Explain  the  dif- 
ference in  the  two. 

2.  Weigh  a  good-sized  potato  and  thoroughly  dry  it  by  heating  in 
an  oven.  Weigh  again.  What  per  cent  of  moisture  did  it  contain  ?  Place 
in  a  crucible  and  heat  to  redness  to  drive  off  the  organic  matter.  What 
per  cent  is  ash  ? 

3.  Thoroughly  water  a  pot  of  young  oat  seedlings  and  turn  a  bell 
jar  over  them.  Account  for  the  drops  of  water  that  soon  appear  on  the 
tips  of  the  leaves.  The  same  experiment  may  be  performed  with  nas- 
turtium or  fuchsia  plants  if  oats  are  not  at  hand. 

4.  Clover  hay  may  yield  three  tons  to  the  acre.  How  many  inches 
of  rainfall  would  be  needed  to  supply  the  necessary  moisture  if  none 
were  wasted  and  the  plants  used  250  pounds  of  water  in  producing 
each  pound  of  dry  matter? 

References 

Hopkins,  "  Soil  Fertility  and  Permanent  Agriculture." 
Snyder,  "  Chemistry  of  Animals  and  Plants." 


CHAPTER  VII 

FERTILIZERS 

The  available  mineral  in  the  soil.  The  elements  needed  by 
plants  exist  in  the  soil  in  very  unequal  proportions.  Some  are 
so  abundant  as  to  be  practically  inexhaustible  ;  others  occur  in 
such  small  quantities,  or  are  so  slowly  weathered  out  of  the 
soil,  that  cropping  for  a  few  years  may  deplete  the  supply  to 
a  point  where  more  must  be  added  before  the  land  will  again 
be  fully  productive.  It  has  been  estimated  that  in  the  upper 
seven  inches  of  certain  soils  there  is  sufficient  iron  to  produce 
a  hundred-bushel  corn  crop  every  year  for  two  hundred  thou- 
sand years,  and  enough  calcium,  sulphur,  and  magnesium  to 
produce  such  crops  for  from  two  thousand  to  fifty  thousand 
years,  but  only  enough  nitrogen  and  phosphorus  for  from  fifty 
to  seventy  years.  Other  soils  may  differ  as  to  the  amounts  of 
each  element  they  contain,  but  the  proportions  are  likely  to 
be  about  as  given  here.  It  is  thus  seen  that  the  soil  is  not  an 
indestructible  asset,  but  that  it  may  easily  wear  out  by  having 
all  its  store  of  certain  elements  abstracted  by  growing  crops. 
Nor  is  it  necessary  that  an  element  be  entirely  lacking  in  a 
soil  to  render  it  unfertile.  If  the  element  be  in  a  form  that  is 
not  available  to  plants,  the  effect  is  the  same  as  if  it  were 
entirely  absent. 

Toxic  substances  in  the  soil.  Occasionally  an  analysis  of 
the  soil  may  show  that  it  contains  sufficient  food  materials  for 
good  crops,  yet  the  plants  that  grow  upon  it  do  not  flourish 
because  of  certain  substances  excreted  by  the  roots  of  the 
plants  themselves,  which  seem  to  be  toxic  or  poisonous  to 
that  particular  crop.    When  crops  of  one  kind  are  grown  for 

101 


102 


AGRONOMY 


several  years  in  succession  upon  the  same  land,  for  instance,  the 
yield  begins  to  decrease  long  before  the  available  mineral  food 
has  been  used  up.  Thrifty  crops  of  the  same  kind  growing 
elsewhere,  if  watered  with  extracts  from  such  soils,  give  every 
evidence  of  having  been  poisoned.  When  supplied  with  cer- 
tain chemical  elements,  however,  they  regain  their  health. 
Many  wild    plants    exhibit    similar    peculiarities,    and    their 


I'niversity  of  Illiuois 

Fig.  83.   Wheat  crop  averaging  9.6  bushels  to  the  acre 

The  soil  has  been  limed  and  a  crop  of  legumes  plowed  under.    Compare  with 
the  following  figure 

inability  to  grow  in  the  same  soil  for  any  length  of  time  is 
attributed  to  an  increase  of  the  toxic  elements.  After  growing 
for  a  year  or  so  in  a  given  spot  the  old  parts  die,  while  the  new 
ones  move  out  from  the  center  in  a  constantly  widenmg  circle 
known  as  a  "  fairy  ring."  Such  rings  are  more  common  in 
fungi,  lichens,  and  ferns,  but  they  also  occur  in  flowering  plants. 
Most  of  these  poisonous  excretions  appear  to  be  harmful  only 
to  the  species  that  produced  them,  which  explains  one  of  the 
benefits  of  a  rotation  of  crops.    By  growing  different  crops  on 


FERTILIZERS 


103 


the  land  the  toxic  substances  excreted  by  one  kind  have  time 
to  escape  or  become  neutralized  before  the  same  crop  is  again 
grown  there.  In  some  cases,  however,  the  excretions  from  one 
set  of  plants  seem  harmful  to  others.  The  butternut  tree  has 
been  found  antagonistic  to  the  shrubby  cinquefoil  that  some- 
times, infests  the  pastures  in  New  England  and  elsewhere, 


Photofjraph  by  the  University  of  Illinois 

Fig.  84.    Wheat  crop  averaging  21.5  bushels  to  the  acre 

This  wheat  was  grown  on  land  adjoining  that  shown  in  preceding  figure.   In  ad- 
dition to  lime  and  legumes  the  soil  has  had  an  application  of  phosphorus 

while  a  similar  antagonism  seems  to  exist  between  grass  and 
certain  fruit  and  shade  trees.  Additions  of  various  substances 
to  the  soil  seem  to  neutralize  these  poisonous  excretions  of 
plants  and  enable  them  to  continue  in  vigorous  growth.  Some 
contend  that  this  is  the  only  value  to  be  derived  from  fertiliz- 
ers. Whatever  the  reason  for  adding  fertilizers,  the  fact  re- 
mains that  good  crops  cannot  long  be  produced  without  them. 
Nor  will  an  excess  of  one  needed  element  compensate  for  the 


104  AGRONOMY 

lack  of  another ;  a  sufficient  amount  of  each  must  be  present. 
Often  supplying  a  single  lacking  element  in  the  soil  will  more 
than  double  the  returns  from  the  crop. 

Elements  that  may  be  lacking.  Soils  are  seldom  deficient  in 
sulphur,  iron,  or  magnesium,  and  calcium  is  usually  abundant 
enough,  though  it  may  sometimes  be  lacking  even  in  soils  de- 
rived from  the  weathering  of  limestone  rocks,  because  it  is 
easily  dissolved  and  carried  off  by  the  water.  Phosphorus,  nitro- 
gen, and  potash,  however,  belong  to  a  different  category.  They 
are  seldom  abundant  in  any  soil  and  are  so  rapidly  removed 
by  crops  that  the  lack  of  one  of  them  is  usually  the  cause  of 
a  decreased  yield.  Soils  may  be  analyzed  by  the  chemist  and 
the  exact  amount  of  each  mineral  constituent  determined,  but 
there  are  various  ways  of  making  the  plants  themselves  tell 
what  essential  element  is  lacking.  One  of  the  best  methods 
of  determining  this  is  to  make  ten  plots,  side  by  side,  in  soil 
as  nearly  uniform  as  possible,  and  add  to  each  plot  a  different 
fertilizer  or  combination  of  fertilizers  containing  the  elements 
likely  to  be  lacking.    The  usual  arrangement  is  as  follows : 

Plot  1.  Nitrogen  as  nitrate  of  soda  at  the  rate  of  160  lb.  to  the  acre,  or 
dried  blood  at  the  rate  of  700  lb.  to  the  acre. 

Plot  2.  Potash  as  muriate  of  potash  at  the  rate  of  80  lb.  to  the  acre,  or 
potassium  sulphate  at  the  rate  of  200  lb.  to  the  acre. 

Plot  3.  Phosi>horns  as  acid  phosphate  at  the  rate  of  320  lb.  to  the  acre, 
or  bone  meal  at  the  rate  of  200  lb.  to  the  acre. 

Plot  4.  Calcium  as  lime  at  the  rate  of  40  bu.  to  the  acre. 

Plot  5.  Nothing.    This  plot  serves  as  a  check  for  comparison. 

Plot  G.  Nitrogen  and  potash  in  the  proportions  given  above. 

Plot  7.  Nitrogen  and  phosphorus  in  the  proportions  given  above. 

Plot  8.  Potash  and  phosphorus  in  the  proportions  given  above. 

Plot  9.  Potash,  phosphorus,  and  nitrogen  in  proportions  as  above. 

Plot  10.  Same  as  Plot  9  with  the  addition  of  lime. 

The  crops  to  be  tested  should  be  sown  across  all  the  plots,  and 
will  soon  show  which  element  is  deficient  by  a  more  thrifty 
growth  in  the  plot  containing  this  element.   It  is  desirable  that 


FERTILIZEKS  105 

different  crops  be  used  in  the  test,  since  the  lacking  element 
may  not  be  the  same  for  each.  In  any  soil  the  need  for  cal- 
cium may  be  easily  discovered  by  treating  part  of  a  field  with 
lime  and  comparing  the  treated  area  with  the  part  not  treated. 
The  lime  should  be  applied  at  the  rate  of  twenty  bushels  or 
more  to  the  acre.  When  red  clover  and  alfalfa  grow  well  on  a 
given  soil,  this  is  a  good  indication  that  it  contains  sufficient 
calcium.  A  growth  of  mosses  indicates  a  lack  of  this  element. 
Sources  of  the  needed  elements.  It  is  only  in  exceptional 
cases  that  the  cultivator  concerns  himself  about  any  element 
in  the  soil  except  potash,  nitrogen,  and  phosphorus.  These 
three  are  seldom  abundant,  and  the  farmer  always  adds  fer- 
tilizers containing  them  when  they  can  be  cheaply  obtained. 
Stable  manure  is  called  a  "  complete  "  fertilizer  because  it  con- 
tains portions  of  all  three.  Before  the  advent  of  the  white 
man  the  Indian  had  discovered  the  value  of  fish  as  a  ferti- 
lizer. Near  the  coast  it  was  the  custom  to  place  a  fish  in  each 
hill  of  corn.  In  many  places  fish  is  still  used  for  fertilizer. 
Several  other  available  sources  of  the  necessary  elements  exist. 
Nitrogen  is  found  in  guano,  fish  guano,  dried  blood,  slaughter- 
house waste,  bone  meal,  linseed  and  cottonseed  meal,  ammo- 
nium sulphate  (a  product  of  gas  works),  potassium  nitrate,  and 
sodium  nitrate,  or  Chile  saltpeter.  The  sodium  nitrate  is  the 
most  soluble.  Potash  is  found  in  wood  ashes,  muriate  of  pot- 
ash, sulphate  of  potash,  and  kainit.  Phosphorus  occurs  in  bones 
and  bone  meal,  phosphate  rock,  and  Thomas  slag,  which  is  a 
by-product  in  the  manufacture  of  steel.  When  necessary  to 
apply  calcium  it  may  be  in  the  form  of  ground  limestone,  quick- 
lime, marl,  gypsum,  shells,  and  bones.  In  applying  fertilizers  it 
is  well  to  remember  that  some  are  more  soluble  than  others  and, 
applied  in  too  great  quantity,  may  easily  make  the  soil  water 
so  dense  as  to  kill  or  greatly  retard  the  plants  it  was  designed 
to  help.  Other  fertilizers,  becoming  available  more  slowly,  may 
not  show  their  effects  upon  the  crops  until  the  second  season. 


106  AGRONOMY 

Manures.  The  word  manure  comes  from  the  Latin  word  manus 
meaning  "  hand."  The  reason  for  the  derivation  is  seen  when 
it  is  known  that  to  manure  originally  meant  to  dig  or  culti- 
vate by  hand.  Thus  in  Defoe's  "  Robinson  Crusoe,"  written 
in  1719,  we  find  the  expression,  "The  ground  that  I  had 
manured,  or  dug  up,  for  them  was  not  great."  Digging  about 
the  plant  was  early  found  to  make  it  more  thrifty,  and  the 
old  farmer's  maxim  that  "  tillage  is  manure "  is  true  in  a 
more  literal  sense  than  he  perhaps  imagines.  "When  it  was 
found  that  adding  various  matters  to  the  soil  had  the  same 
effect  upon  the  plants  as  cultivation,  these  substances  soon 
gained  the  name  of  "  manures." 

Green  manures.  Frequently  the  cultivator  plows  under  a 
growing  crop  for  the  purpose  of  adding  humus  and  its  con- 
tained nitrogen  to  the  soil.  Such  additions  are  known  as 
green  manures.  Barley,  turnips,  and  similar  crops,  and  even 
weeds,  may  be  used  for  this  purpose,  but  clover,  alfalfa,  and 
other  legumes  are  usually  relied  upon.  These  latter  bear 
upon  their  roots  numerous  small  nodules  containing  bacteria 
which  are  capable  of  fixing  atmospheric  nitrogen  in  the  soil, 
and  are  therefore  especially  valuable  for  such  purposes. 
Legumes  actually  leave  the  soil  in  better  condition  than  they 
find  it. 

Nitrification.  Undoubtedly  the  most  important  single  ele- 
ment of  plant  food  is  nitrogen.  This  element  is  not  found 
in  combination  in  the  rocks  because  it  is  too  inert  to  readily 
combine  with  other  elements,  and  the  large  quantities  in  the 
air  are  not  available  to  ordinary  plants,  though  some  species 
are  believed  to  be  able  to  absorb  nitrogen  from  the  ariimonia 
in  the  air  through  their  leaves.  Small  amounts  of  both  am- 
monia and  nitric  acid  may  be  added  to  the  soil  by  being  brought 
down  from  the  air  in  ram  water  or  snow  and  converted  into 
plant  food  by  the  soil  bacteria,  but  the  amount  thus  added  to 
the  soil  is  too  insignificant  to  make  it  important  as  a  source 


FERTILIZEKS  107 

of  nitrogen  to  plants.  Practically  all  the  nitrogen  used  by 
plants  comes  from  the  humus  m  the  soil.  Nor  can  the  plant 
use  all  the  combinations  of  nitrogen  derived  from  humus. 
In  the  soil  this  element  may  exist  as  ammonia,  nitrites,  and 
nitrates,  but  plants  can  use  only  the  nitrates. 

Bacteria  and  nitrification.  The  changing  of  nitrogenous 
substances  in  the  humus  to  forms  that  are  available  to  plants 
is  accomplished  by  bacteria,  of  which  there  are  some  fifty 
million  in  every  cubic  centimeter  of  rich  soil.  These  bacteria 
are  the  smallest  of  livmg  things.  They  are  most  numerous 
near  the  surface  of  the  soil,  but  are  found  in  lessened 
numbers  as  far  down  as  the  lowest  layers  of  the  subsoil. 
Like  other  plants,  they  need  warmth,  moisture,  and  oxygen 
for  growth,  but,  unlike  them,  must  have  organic  food.  They 
are  very  intolerant  of  acids  and  will  not  live  in  sour  soils. 
In  bogs  and  other  water-soaked  soils  the  absence  of  air  pre- 
vents the  growth  of  bacteria,  the  soil  becomes  sour  by  the 
accumulation  of  acids  from  the  dead  vegetation,  and  the 
organic  material,  instead  of  being  turned  to  nitrates,  forms 
peat.  The  addition  of  lime  to  such  soils  corrects  the  acidity, 
but  draining  is  necessary  to  promote  the  activities  of  the 
bacteria.  The  fertility  of  the  soil  is  then  effected  exactly  as 
it  would  be  by  the  addition  of  more  nitrogen. 

Three  sets  of  bacteria  are  concerned  in  the  work  of  nitrifi- 
cation. The  first  group  simply  turns  the  nitrogenous  parts 
of  the  humus  to  ammonia,  a  process  which  is  often  called 
ammonification.  In  this  process  the  animal  and  vegetable 
matter  in  the  soil  serves  as  food  for  the  bacteria  which  may 
be  said  to  digest  it,  excreting  ferments,  or  enzymes,  for  the 
purpose.  Considerable  carbon  dioxide  is  also  liberated  in  this 
process,  and  this  serves  to  further  weather  the  soil  particles. 
The  ammonia  produced  by  the  bacteria  combines  with  soil 
water  to  form  ammonium  hydroxide  (NH^OH),  and  at  this 
point  a  new  group  of  bacteria,  known  as  Nitrosococcris,  turns 


108 


AGRONOMY 


the  ammonium  hydroxide  into  nitrous  acid  and  hydrogen  by  the 
addition  of  an  atom  of  oxygen  (NH^OH  +  O  =  HNO^,  +  H^). 
The  nitrous  acid  combining  with  various  minerals  in  the  soil 
form  nitrites,  and  a  third  set  of  bacteria,  of  the  genus  Nitro- 
bacter,  now  adds  another  atom  of  oxygen  to  this  compound, 
forming  the  nitrates  used  by  plants.  Although  nitrites  and 
nitrates  differ  principally  in  the  possession  of  one  more  atom 
of  oxygen  by  the  latter,  plants  seem  able  to  use  only  the 
nitrates.  Nitrobacter^  so  far  as  known,  is  the  only  bacterium 
that  can  turn  nitrites  into  nitrates. 

Nitrogen  fixation.  Certam  plants  known  as  legumes,  of 
which  the  bean,  pea,  clover,  and  alfalfa  are  examples,  have  the 
power  to  fix  atmospheric  nitrogen,  or,  rather,  they  have  set  up 

a  partnership  with  bac- 
teria which  are  able  to 
do  so.  In  this  partner- 
ship the  bacteria  (Psew- 
domonas  radicicola),  in 
return  for  the  carbohy- 
drates which  they  need, 
give  to  the  legumes  the 
nitrogen  which  they  are 
able  to  take  from  the 
air.  Such  a  partnership  as  this  is  called  symbiosis,  and  the  part- 
ners are  known  as  symbionts.  Certain  alga?  in  the  soil  seem 
also  to  have  entered  into  symbiotic  relations  with  bacteria  for 
the  purpose  of  getting  nitrogen.  By  carefully  digging  up 
any  legume  and  washing  off  the  soil  clinging  to  the  roots  the 
nodules  which  the  bacteria  inhabit  are  easily  seen.  Another 
bacterium,  Azotobacter  chroococcum,  appears  to  be  able  to  fix 
atmospheric  nitrogen  by  itself,  oxidizing  carbohydrates  in  the 
soil  in  the  process.  The  fact  that  lands  allowed  to  lie  without 
cultivation,  or  fallow,  for  a  time,  increase  in  nitrogen  content 
is  attributed  to  the  presence  of  this  and  other  bacteria.    The 


Fig.  85.    Nodules  on  the  roots  of  a  leorume 


FEETILIZERS 


109 


fixing  of  nitrogen,  however,  cannot  go  on  without  lime.  Owing 
to  the  power  of  their  bacterial  symbiont  to  fix  nitrogen  from 
the  air,  legumes  are  able  to  thrive  in  soils  too  poor  in  nitrogen 
to  support  other  crops.  In  sandy  regions,  where  the  loose  and 
open  soil  permits  the  loss  of  nitrates  almost  as  fast  as  formed, 
legumes  are  usually  abundant. 

Mycorrhizas.  In  a  considerable  number  of  plants,  among 
which  are  various  trees  and  shrubs,  the  older  parts  of  the 
roots  are  inhabited  by  fungi  known 
as  mycorrJiizas,  which  enter  into  sym- 
biosis with  them.  Such  associations 
are  common,  or  possibly  the  rule, 
among  woody  plants,  but  are  espe- 
cially abundant  in  the  heath  family, 
to  which  the  rhododendron,  cranberry, 
and  blueberry  belong.  The  mycor- 
rhizas extend  out  into  the  soil  and 
function  like  root  hairs.  They  appear 
to  have  the  power  to  fix  nitrogen 
from  the  humus  in  the  soil  and  ab- 
sorb sugars  derived  from  fallen  leaves 
by  other  soil  bacteria.  Certain  flow- 
ering plants,  like  the  Indian  pipe  and 
the  pinesap,  which  lack  chlorophyll,  ab- 
sorb all  their  food  in  this  way.  Mycor- 
rhizas are  also  frequently  associated 
with  plants  that  transpire  slowly; 
otherwise  these  plants  would  find 
difficulty  in  getting  sufficient  food. 

Soil  inoculation.  In  many  soils  it  is  difficult  to  get  a  good 
crop  of  legumes  because  the  necessary  bacteria  for  symbiosis 
do  not  occur  there.  Experiments  seem  to  show  that  each 
species  of  legume,  if  it  does  not  have  its  own  special  bacterial 
species,  has  at  least  a  special  form  with  which  it  is  associated, 


Fig.  86.    The  snow  plant 
{Sarcodes  sanguinea) 

A      saprophytic      heathwort 

(alMed    to   the   Indian   pipe, 

Monotropa     uniflora)     from 

the  Pacific  Coast  region 


110  AGRONOMY 

and  wlien  this  is  missing  it  cannot  thrive.  In  some  cases, 
however,  the  form  of  bacteria  associated  with  one  species  may 
be  gradually  induced  to  form  partnersliips  with  another. 
When  the  necessary  bacteria  are  lacking,  the  soil  may  be  inocu- 
lated by  a  few  bushels  of  soil  brought  from  another  field  in 
which  the  desired  crop  grows  well.  This  is  scattered  over 
the  field  at  the  time  of  planting  exactly  as  one  would  scatter 
seeds.  In  a  few  instances  the  bacteria  of  two  species  seem  to 
be  interchangeable.  Fields  in  which  red  clover  or  alfalfa  will 
not  grow  because  their  bacterium  is  absent,  may  be  made  to 
produce  these  crops  by  inoculating  with  soil  brought  from 
the  nearest  patch  of  wild  sweet  clover.  In  the  same  way  the 
bacterial  symbiont  of  cowpeas  may  be  supplied  from  soils  in 
which  the  wild  partridge  pea  occurs.  Several  attempts,  more 
or  less  successful,  have  been  made  by  the  national  govern- 
ment and  by  private  parties  to  send  out  dormant  cultures  of 
bacteria  for  use  with  certain  crops.  The  seeds  of  the  crop 
desired  are  inoculated  with  the  bacteria  before  sowing.  In 
the  case  of  many  cultivated  species  of  legumes,  and  possibly 
all  wild  ones,  the  bacteria  with  which  they  form  associations 
are  transported  into  new  soils  by  clinging  to  the  seeds. 

Denitrifying  bacteria.  Along  with  the  bacteria  in  the  soil 
which  turn  nitrogenous  substances  to  nitrates  are  found  other 
bacteria  which  reverse  the  process,  and,  by  extracting  the 
oxygen  from  nitrates,  set  free  the  nitrogen.  This  process 
goes  on  most  rapidly  in  soils  which  are  not  properly  aerated. 
Stable  manure,  left  in  piles,  loses  much  nitrogen  in  this  way. 
When  plenty  of  oxygen  is  present  the  bacteria  do  not  attack 
the  nitrates. 

Harmful  organisms  in  the  soil.  As  we  have  seen,  the  living 
elements  of  the  soil  are  quite  as  important  as  its  mineral 
constituents.  In  addition  to  the  nitrifying  and  denitrifying 
bacteria  and  the  nitrogen-fixing  bacteria,  there  are  many 
yeasts,  algai,  fungi,  germs  of  plant  diseases,  and  hosts  of 


FERTILIZERS  111 

protozoa.  The  protozoa  are  one-celled  animals  that  feed  upon 
the  helpful  bacteria,  often  to  such  an  extent  as  to  effect  the 
fertility  of  the  soil.  These  may  be  killed  or  reduced  in 
numbers  by  burning  or  boiling  the  soil,  or  by  treating  it  with 
disinfectants.  Such  treatment  does  not  appear  to  materially 
harm  the  bacteria.  The  increase  in  fertility  in  soils  burned 
over  is  attributed  to  the  fact  that  the  burning  killed  the 
protozoa.  Florists  usually  bake  the  soil  hi  which  young 
seeds  are  to  be  sown,  or  they  may  pour  boiling  water  over  it, 
and  in  this  way  get  rid  of  the  harmful  organisms  in  it. 

Limiting  factors  in  plant  growth.  The  production  of  the 
maximum  crop  is  thus  seen  to  depend  on  many  things  besides 
a  sufficient  amount  of  the  necessary  chemical  elements  in  the 
soil.  The  temperature  may  be  too  high  or  too  low,  there 
may  be  too  little  sunshine  at  some  critical  period  of  plant 
growth,  or  the  soil  itself  may  contain  too  much  or  too  little 
moisture.  Any  unfavorable  condition  at  once  becomes  the 
limiting  factor  in  plant  growth,  and  changing  this  condition 
frequently  results  in  doubling  or  trebling  the  crop.  In  the 
West  water  is  often  the  limiting  factor,  but  under  irrigation 
or  in  regions  of  sufficient  rainfall  the  lack  of  some  mineral 
constituent  of  the  soil  is  likely  to  prevent  the  maximum  yield. 
The  presence  of  insects  or  plant  diseases  may  also  affect  the 
crop,  and  thus  the  limiting  factor  may  even  change  from  year 
to  year,  with  favorable  or  unfavorable  seasons.  By  supplying 
the  soil  with  sufficient  fertilizers  and  regulating  by  irriga- 
tion, drainage,  and  cultivation  the  amount  of  moisture  in  it, 
the  farmer  renders  favorable  such  conditions  as  can  be  con- 
trolled, which  fortunately  are  among  the  most  important.  The 
photographs  on  pages  102  and  103  illustrate  very  clearly  the 
change  that  may  result  from  adding  a  single  chemical  element 
to  the  soil.  Here  the  application  of  a  fertilizer  containing 
phosphorus  had  the  effect  of  immediately  adding  nearly  twelve 
bushels  an  acre  to  the  crop. 


112  AGRONOMY 

PRACTICAL  EXERCISES 

1.  Make  an  expedition  to  the  fields  and  woods  for  evidences  of 
"  fairy  rings." 

2.  In  the  experiment  garden  make  a  test  of  the  soil  as  directed  on 
page  104. 

3.  Make  a  collection  of  all  of  the  commercial  fertilizers.    Label. 

4.  Make  a  list  of  all  the  legumes,  cultivated  or  wild,  that  can  be 
found  in  the  school  garden. 

5.  Make  a  list  of  the  wild  legumes  of  the  region. 

6.  Make  up  an  extract  of  rich  soil  by  soaking  it  in  water.  Put  a 
drop  of  the  turbid  water  on  a  slide  and  examine  with  the  high  power  of 
the  microscope  for  the  bacteria. 

7.  Dig  up  clover  or  other  legumes  and  look  for  the  nodules  on  their 
roots. 

8.  Crush  a  nodule  and  examine  it  under  the  microscope. 

9.  What  is  the  limiting  factor  of  plant  growth  in  your  region  ? 

References 

Hopkins,  "  Soil  Fertility  and  Permanent  Agriculture." 

Roberts,  "The  Fertility  of  the  Land." 

Voorhees,  "Fertilizers." 

"Warren,  "  Elements  of  Agriculture." 

Farmers?  BuUetins 

16.  Leguminous  Plants. 

31.  Alfalfa  or  Lucerne. 

44.  Commercial  Fertilizers. 

77.  The  Liming  of  Soils. 

89.  Cowpeas. 
123.  Red  Clover  Seed. 
144.  Rotation  of  Crops. 
192.  Barnyard  Manure. 
237.  Lime  and  Clover. 
245.  Renovation  of  Worn-out  Soils. 
278.  Leguminous  Crops  for  Green  Manuring. 

Bureau  of  Plant  Industry 

71.  Soil  Inoculation  for  Legumes. 
173.  Seasonal  Nitrification  as  influenced  by  Crops  and  Tillage. 


CHAPTER  VIII 

THE  PLANT  IN  RELATION  TO  TEMPERATURE,  LIGHT,  AND 
MOISTURE 

Growth  temperature.  The  range  of  temperature  that  vege- 
tation in  the  aggregate  can  endure  is  remarkable.  Seeds  in 
the  dormant  condition  have  been  exposed  to  the  temperature 
of  liquid  air,  many  degrees  below  zero,  without  impairing 
their  vitality ;  and,  on  the  other  hand,  some  algae  can  exist  in 
hot  springs  where  the  temperature  of  the  water  reaches  nearly 
to  the  boiling  point.  No  single  species,  however,  can  endure 
anything  like  this  range  of  temperature.  Ordinary  plants  are 
balanced  midway  between  two  rather  close  extremes  of  heat 
and  cold,  growing  well  so  long  as  neither  is  too  closely 
approached,  going  into  a  dormant  condition  when  brought 
nearer,  and  dying  when  either  extreme  is  reached.  Differ- 
ences in  temperature  are  among  the  principal  factors  control- 
ling the  distribution  of  plants.  Elevated  country  and  mountain 
ranges  act  as  barriers  to  the  spread  of  tropical  plants,  because 
the  upper  regions  are  cold,  and  a  stretch  of  warm  lowland  may 
prevent  the  migration  of  alpine  vegetation  from  one  summit 
to  another;  in  fact,  there  is  scarcely  a  species  that  is  not 
sharply  limited  in  some  part  of  its  range  by  temperature. 

A  temperature  of  122°  above  zero  is  fatal  to  most  land 
plants  in  the  growing  condition,  and  aquatics  usually  perish 
at  somewhat  lower  temperatures.  Plants  and  plant  parts  gen- 
erally can  endure  the  greatest  amounts  of  heat  and  cold  when 
they  contain  the  least  water.  In  seeds,  developed  by  the  plants 
for  carrying  them  over  unfavorable  seasons,  the  protoplasm 
is  brought  to  the  resting  and  more  resistant  condition  by  the 

113 


114  AGRONOMY 

exclusion  of  most  of  the  moisture.  Some  hardy  arctic  plants, 
however,  can  be  frozen  and  thawed  several  times  a  day  during 
the  growing  season  without  being  injured. 

The  plants  of  a  given  region  have  their  own  peculiarities 
in  the  matter  of  the  temperature  at  which  growth  processes 
begin.  In  the  arctics  certain  seaweeds  thrive  in  water  that 
seldom  rises  above  32°,  and  are  easily  killed  by  temperatures 
a  few  degrees  higher.  Most  plants  of  the  temperate  zone  will 
begin  to  grow  at  about  41°  above  zero,  and  some,  such  as 
oats,  wheat,  rye,  and  peas,  can  make  some  growth  when  the 
temperature  is  just  above  the  freezing  point;  but  the  best  tem- 
perature for  germination  is  between  60°  and  70°,  and  many 
species,  even  in  the  colder  parts  of  the  world,  will  not  start 
to  grow  until  such  temperatures  are  reached.  Up  to  a  certain 
point  heat  seems  to  stimulate  growth  processes  just  as  it  does 
chemical  reactions.  In  the  tropics  the  temperature  at  which 
seeds  germinate  is  usually  ten  or  twelve  degrees  higher  than 
that  required  for  more  northern  plants,  the  most  desirable  being 
between  70°  and  80°.  The  seeds  of  many  tropical  species, 
when  planted  in  our  hothouses,  must  be  given  a  temperature 
above  90°  to  get  the  best  results.  These  facts  explain  why 
some  seeds  are  planted  earlier  than  others.  Peas  and  spinach 
are  cool-weather  plants  and  may  be  planted  as  soon  as  the 
ground  can  be  worked  in  spring ;  indeed,  unless  the  season 
is  fairly  cool  these  crops  do  not  do  well.  Corn  and  tomatoes, 
on  the  other  hand,  which  came  originally  from  the  tropics, 
must  wait  until  both  the  soil  and  air  are  thoroughly  warmed. 

Hardy  and  tender  plants.  As  regards  the  sensitiveness  of 
the  plants  to  cold,  gardeners  are  accustomed  to  group  them 
as  hardy,  half-hardy,  and  tender  species.  Hardy  plants  are 
those  that  endure  the  winter  season  unharmed.  The  perennial 
plants  of  any  region  are  necessarily  hardy  plants.  Half-hardy 
plants  are  those  that  need  artificial  protection  during  the 
winter,  though  in  mild  seasons  they  may  survive  without  this. 


TEMPERATURE,  LIGHT,  AND  MOISTURE       115 

Tender  plants  are  those  that  die  as  soon  as  frost  comes. 
These  are  general  terms,  however,  and  indicate  relative  con- 
ditions only,  since  a  plant  that  is  perfectly  hardy  in  one 
region  may  be  only  half  hardy  or  even  tender  in  a  colder  one. 
On  the  other  hand,  the  trees  that  are  deciduous  in  cold  regions 
may  become  evergreen  when  removed  to  warm  regions.  Vio- 
lets, which  flower  for  only  a  few  weeks  in  spring  in  the 
Northern  states,  may  bloom  throughout  the  autumn,  winter, 
and  spring  near  the  Gulf. 

Cardinal  points.  As  has  been  indicated,  there  are  three 
important  temperature  points  for  every  species  of  plant:  the 
minimum,  or  lowest  point  at  which  growth  processes  can  pro- 
ceed ;  the  maximum,  or  highest  point  at  which  growth  is  possi- 
ble ;  and  the  optimum,  or  most  favorable  temperature.  These 
points  are  called  cardinal  points,  or  the  upper,  middle,  and  lower 
zeros.  They  are  not  the  same  for  all  plants,  and  in  general  are 
higher  for  tropical  plants  than  for  those  of  temperate  regions. 
Each  species  may  also  have  a  different  maximum,  minimum, 
and  optimum  for  its  vegetative  and  reproductive  processes.  In 
such  cases  the  cardinal  points  for  growth  are  usually  higher 
than  those  for  reproduction.  The  large  number  of  species  that 
flower  in  early  spring,  often  before  the  leaves  have  appeared, 
are  instances  of  this  fact. 

Acclimatization.  Some  plants  of  tropical  regions  can  be 
induced  to  grow  much  farther  north  than  they  occur  in  nature, 
and  the  same  is  true  with  respect  to  northern  plants  in  more 
southern  regions.  The  adaptation  of  plants  to  such  conditions 
is  called  acclimatization.  Complete  acclimatization  is  possible 
only  with  plants  that  are  able  to  make  new  adjustments  of 
their  cardinal  points,  raising  or  lowering  them  to  fit  the  new 
conditions.  Sometimes  the  vegetative  point  may  be  thus 
changed,  but  not  that  for  reproduction,  in  which  case  the 
plant  may  produce  plenty  of  stems  and  leaves,  but  no  flowers 
or  fruits.   Our  most  persistent  and  successful  weeds  are  largely 


116  AGEONOMY 

so  because  of  the  facility  with  which  they  are  able  to  make 
new  adjustments  of  their  cardinal  points. 

Frost.  The  air  always  contains  some  moisture,  and  the 
warmer  the  air  the  more  it  can  contain.  When  it  contains  all 
that  it  will  hold  at  a  given  temperature,  it  is  said  to  be  satu- 
rated. If  the  temperature  of  moist  air  be  lowered  beyond  the 
saturation  point,  some  of  the  moisture  has  to  be  dropped.  If 
this  occurs  in  the  air,  the  dropped  moisture  is  called  rain  or 
fog;  if  deposited  on  the  earth,  it  is  deiv  or  frost.  The  point 
at  which  the  water  begins  to  condense  out  of  the  air  is  called 
the  dew  point.  Frost  differs  from  dew  only  in  that  it  is  depos- 
ited at  temperatures  below  the  freezing  point  of  water.  There 
is  always  danger  of  frost  when  the  weather  report  predicts 
temperatures  eight  or  ten  degrees  above  freezing,  since  in  any 
given  locality  the  temperature  may  fall  a  few  degrees  below 
that  predicted.  A  still  clear  night  favors  the  formation  of 
frost  by  promoting  the  cooling  of  the  earth  and  air  by  radia- 
tion. When  the  sky  is  cloudy,  the  clouds,  like  a  blanket,  keep 
in  the  heat.  A  fog  at  night,  or  much  smoke  or  dust  in  the  air, 
protects  in  the  same  way.  A  windy  night  may  also  protect 
from  frost  by  moving  the  cold  air  about  and  keeping  it  from 
settling  down  in  any  one  place. 

Locality  and  frost.  Danger  from  frost  is  not  confined  to 
northern  latitudes.  In  any  region  where  the  temperature  goes 
below  the  freezing  point  there  is  danger  from  late  spring  and 
early  autumn  frosts.  The  location,  however,  often  has  much 
to  do  with  immunity  from  frost.  In  the  vicinity  of  large  bodies 
of  water  frosts  are  often  long  delayed  in  autumn  because,  as 
the  temperature  lowers,  the  water  gives  off  the  heat  absorbed 
during  the  summer  and  thus  keeps  the  surrounding  air  warm. 
In  rooms  or  cellars  where  the  temperature  might  fall  below 
the  freezing  point,  this  may  be  prevented  by  exposing  therein 
tubs  of  water  which  will  give  off  heat  in  the  same  way.  Cold 
air  is  heavier  than  warm  air  and  tends  to  settle  in  the  hollows 


TEMPERATURE,  LIGHT,  AND  MOISTURE       117 

and  displace  the  warm  air  there.  In  consequence  frost  often 
visits  the  bottom  lands  long  before  it  touches  the  hilltops, 
because  the  latter  are  nightly  bathed  in  the  warm  air  crowded 
up  from  below.  For  this  reason  farmers  usually  plant  the  late 
crops  of  buckwheat  on  the  hillsides.  In  certain  valleys  there 
is  a  zone  part  way  up  the  slope,  called  the  verdant  zone  or 
thermal  belt,  in  which  late  spring  and  early  autumn  frosts  are 
almost  unknown.  This  zone  is  due  to  the  movement  of  the 
warm  air  out  of  the  valley  at  night.  Other  inclosed  valleys 
drained  by  a  stream  may  be  nearly  exempt  from  frost  because 
the  cold  air  flows  away  over  the  stream.  This  distribution  of 
temperature  has  a  curious  effect  upon  the  distribution  of  plants. 
Northern  plants  are  usually  found  farthest  south  in  the  val- 
leys, and  southern  plants  farthest  north  on  the  hillsides,  exactly 
the  opposite  of  what  at  first  glance  one  would  assume  to  be 
the  natural  occurrence. 

How  cold  kills  plants.  Some  tropical  plants  are  so  sensitive 
to  cold  that  they  may  be  killed  by  exposure  to  temperatures 
several  degrees  above  the  freezing  point,  but  usually  plants 
are  killed  by  the  freezing  of  the  protoplasm  or  the  sap  within 
the  cells.  Freezing  of  the  cell  sap  takes  place  at  a  tempera- 
ture somewhat  lower  than  32°,  since  water  containing  dissolved 
substances  requires  a  greater  degree  of  cold  to  congeal  it  than 
does  pure  water.  Often  it  is  not  the  mere  cold  that  kills  plants, 
but  rather  the  withdrawal  of  moisture  from  the  cell  by  the 
formation  of  ice  crystals  in  the  intercellular  spaces.  In  such 
cases  the  effects  of  cold  are  exactly  the  same  as  those  of  dry- 
ing. Otherwise  hardy  plants  are  often  killed  in  winter  by  the 
heaving  due  to  the  alternate  freezing  and  thawing  of  the  soil 
and  the  consequent  breaking  of  the  roots. 

Other  effects  of  cold.  In  plants  that  are  not  killed  outright 
by  the  cold,  the  lowered  temperature  may  injure  the  less 
resistant  parts.  Some  plants,  such  as  the  catalpa,  grape,  rasp- 
berry, and  sumac,  continue  to  grow  until  stopped  by  the  cold, 


118  AGRONOMY 

and  the  stems  do  not  form  strong  buds  at  the  tip.  In  these 
the  buds  and  stems  are  usually  killed  back  several  inches 
annually.  Flower  buds  that  are  formed  in  autumn  are  often 
killed  by  the  cold,  especially  by  a  cold  interval  in  late  spring 
after  they  have  started  into  growth.  Flowers,  of  course,  are 
sensitive  to  cold  and  may  fail  to  set  fruit  even  if  the  temper- 
ature does  not  fall  to  the  freezing  pomt.  In  severe  winters 
the  trunks  of  trees  are  often  split  open  by  the  cold.  Another 
effect  of  the  cold  is  seen  in  the  improvement  in  the  flavor  of 
certain  vegetables  such  as  salsify  and  parsnips. 

How  plants  avoid  the  effects  of  cold.  Most  perennial  plants 
have  devised  various  ways  of  protecting  their  more  delicate 
parts  from  the  cold.  A  large  number  have  developed  the 
geophilous,  or  subterranean,  habit,  and  at  the  approach  of  cold 
weatlier  the  parts  above  ground  die  and  the  life  of  the  plant 
retreats  to  the  underground  parts.  Examples  are  seen  in  the 
species  that  produce  bulbs,  corms,  tubers,  rhizomes,  and  sim- 
ilar structures.  The  same  arrangement  also  protects  from 
drought.  Bulbous  plants  are  always  plentiful  in  dry  regions. 
Plants  above  ground  have  other  means  of  protection.  The 
trees  protect  the  living  cambium  by  a  thick  and  nearly  water- 
proof bark,  and  their  buds  are  protected  by  scales,  hairs,  and 
varnish.  Most  of  the  broad-leaved  trees  drop  their  leaves  to 
avoid  transpiration,  but  the  pines  and  their  allies  with  needle- 
shaped  leaves  that  do  not  transpire  much  are  not  obliged  to  do 
so.  The  twigs  and  stems  of  many  plants  have  a  dense  coating 
of  scales,  epidermal  hairs,  or  wax,  as  an  additional  protection. 
How  effective  epidermis  and  bark  are  in  retainmg  moisture 
in  the  plant  may  be  seen  by  comparing  the  behavior  of  a 
peeled  apple  or  potato  with  that  of  one  in  its  natural  state. 
Herbs  that  retain  their  leaves  adopt  the  rosette  habit,  and  thus 
their  leaves,  close  to  the  earth,  are  protected  all  winter  by  the 
dead  vegetation  and  the  snow.  The  majority  of  these  devices, 
it  may  be  noted,  are  not  so  much  protections  from  the  cold 


TEMPERATURE,  LIGHT,  AND  MOISTURE       119 

as  they  are  means  of  avoiding  the  injuries  likely  to  be  caused 
by  sudden  changes  of  temperature.  On  the  other  hand,  the 
dark  colors  of  bud  scales  readily  absorb  heat  in  sunshine  and 


Fig.  87.   Epidermal  hairs  and  scales.    (Much  enlarged) 

^.mullein;  Z?,  geranium ;  C,  deutzia;  Z),  hollyhock;  £,  dame's  violet; 
F,  shepherdia 

may  thus  increase  the  temperature  of  the  buds  during  the 
cool  days  of  early  spring. 

Artificial  protection  from  the  cold.  Snow  is  of  such  great 
value  as  a  protection  of  plants  in  winter  that  it  is  frequently 
called  "  the  poor  man's  manure."  Wmters  in  which  there  is 
little  snow  are  very  trying  to  plants  because  they  are  left  un- 
protected and  are  thus  easily  heaved  by  the  frost.  Man  often 
adds  to  the  natural  protection  of  plants  by  mulching,  shading, 


120  AGRONOMY 

windbreaks,  and  cold  frames.  Mulching  is  simply  adding  to 
the  cover  of  dead  leaves  with  which  the  ground  is  naturally 
protected  in  winter.  Any  loose  litter  Ls  good  for  this  purpose. 
Straw,  leaves,  and  stable  manure  are  the  materials  most  fre- 
quently used.  In  addition  to  protecting  plants  from  being 
heaved  by  the  cold,  a  mulch  retards  the  thawing  of  the  ground 
in  spring  and  thus  holds  back  early  plants  that  might  other- 
wise be  injured  by  late  frosts.  Windbreaks  are  belts  of  trees, 
usually  evergreens,  planted  on  the  windy  side  of  gardens  and 
fields  to  protect  them  from  the  high  winds  of  winter  and  early 
spring.  In  nature  the  forest  acts  as  a  natural  cover  for  a  vast 
number  of  plants.  Cold  frames  are  frames  of  wood  covered 
with  glass  or  thin  cloth,  which  are  sometimes  placed  over 
plants.  They  are  either  sunk  in  the  ground  to  the  level  of  the 
soil,  or  are  banked  up  with  manure.  On  very  cold  nights  they 
are  covered  with  mats  as  an  additional  protection.  Sprinkling 
plants  with  cold  water  may  protect  them  from  frost  when  the 
temperature  does  not  go  much  below  the  freezing  point.  In 
orchard  practice  the  blooming  trees  are  often  protected  from 
late  spring  frosts  by  smudge  fires,  which  give  off  great  quan- 
tities of  smoke  that  act  like  clouds  in  keeping  the  earth  wami. 

Treatment  of  frostbitten  plants.  Plants  that  have  been 
frostbitten  may  often  be  saved  by  gradual  thawing,  especially 
in  cases  where  the  injury  is  due  to  a  withdrawal  of  moisture 
from  the  cell.  If  possible,  such  plants  should  be  removed  at 
once  to  a  cool  cellar,  sprinkled  with  water,  and  kept  out  of 
the  direct  rays  of  the  sun  for  a  few  days.  Out  of  doors  the 
plants  may  be  sprinkled  with  water  and  protected  from  the 
sunlight.  Frostbitten  plants  and  fruits  should  be  handled  as 
little  as  possible  until  thawed. 

Effects  of  heat.  The  first  noticeable  effect  of  great  heat 
upon  the  plant  is  the  wilting  due  to  increased  evaporation. 
As  the  temperature  rises,  the  plant  is  called  upon  for  more 
and  more  moisture  until  a  point  is  reached  where  the  demand 


TEMPEKATURE,  LIGHT,  AND  MOISTURE       121 

is  greater  than  the  roots  can  supply,  and  the  drooping  of  the 
fohage  ensues.  If  this  continues  long  enough,  it  may  cause 
the  death  of  the  plant,  though  in  bright  sunshine  a  great 
many  plants  wilt  during  the  hottest  part  of  the  day  and 
revive  as  the  temperature  falls.  The  watery  parts  of  plants, 
especially  the  fruit  and  young  leaves,  being  less  resistant  to 
heat  than  the  rest  of  the  plant,  are  often  destroyed  by  exposure 
to  the  hot  sun.  Evergreens  and  other  plants  are  sometimes 
winterkilled,  not  so  much  by  the  cold  as  by  a  sudden  spell  of 
warm  weather  that  calls  upon  stem  and  leaves  for  more  mois- 
ture than  they  can  spare  at  a  time  when  the  roots  are  only 
feebly  absorbing. 

Protection  from  heat.  Since  the  direct  rays  of  the  sun  are 
more  harmful  than  the  heated  air,  tender  specimens  may  be 
protected  in  a  measure  by  screens  of  thin  cloth,  paper,  brush, 
or  lath.  Newly  transplanted  specunens  are  often  sheltered  by 
old  newspapers  or  by  a  broad  leaf,  such  as  that  of  the  burdock 
or  rhubarb.  In  all  such  shading  it  is  well  to  provide  for  a 
circulation  of  air  under  the  cover.  Plants  in  greenhouses  and 
the  like  are  usually  shaded  by  covering  the  underside  of  the 
glass  with  whitewash.  Evergreens  and  other  plants  that  are 
not  perfectly  hardy  will  often  best  endure  the  winter  if  planted 
on  the  north  side  of  buildings  or  in  places  where  the  direct 
sunshine  may  be  avoided. 

The  plants  themselves  have  various  devices  which  protect 
them  from  the  heat.  The  leaves  of  species  exposed  to  the  sun 
are  frequently  covered  with  a  dense  coat  of  hairs  or  scales 
which  shade  the  tender  cells.  On  a  hot  day  the  leaves  of 
corn  roll  up  and  thus  expose  a  smaller  surface  for  evaporation. 
The  prickly  lettuce,  the  compass  plant,  and  the  eucalyptus 
turn  the  e^ges  of  their  leaves  to  the  sun,  and  many  tropical 
species  shed  part  or  all  of  their  leaves  during  the  season  of 
greatest  heat.  The  acacias  and  many  other  plants  of  the  pea 
family,  with  branched  leaves,  alter  the  position  of  their  leaflets 


122  AGRONOMY 

to  avoid  the  heat,  while  in  various  other  plants  the  chloro- 
plasts  are  able  to  change  their  position  in  the  cell. 

Need  of  light.  Light  is  necessary  for  the  existence  of  every 
independent  plant,  since  the  energy  for  food  making  is  derived 
from  this  source.  The  general  effect  of  light  upon  plants,  how- 
ever, is  to  inhibit  growth,  and  chlorophyll  itself,  the  very  sub- 
stance by  means  of  which  the  chloroplasts  turn  sunlight  into 
useful  energy,  is  broken  down  in  strong  light.  Bacteria  soon 
die  when  exposed  to  direct  sunlight,  and  many  of  the  higher 
plants  cannot  live  long  under  such  conditions.  These  latter 
grow  in  forests,  ravines,  and  other  secluded  places  and  are 
known  as  aliade  plants.  F'erns  and  many  of  the  plants  that 
bloom  in  early  sprmg  are  shade  plants.  Many  of  our  forest 
trees  are  essentially  shade  plants  when  young.  Absence  of 
sufficient  light,  however,  is  quite  as  bad  as  too  much.  In  in- 
sufficient light  the  formation  of  wood  cells  entirely  ceases. 
As  in  the  case  of  temperature,  the  plant  is  balanced  between 
two  harmful  extremes. 

Effects  of  lack  of  light.  Sun-loving  plants  grown  in  deep 
shade  are  deficient  in  chlorophyll,  and  have  small  leaves  and 
weak  stems  which  are  greatly  elongated,  or  "  drawn."  The 
flowers  are  also  paler  and  the  fruit  scanty  and  lacking  in  flavor. 
Aromatic  plants  have  their  aromatic  properties  lessened  when 
grown  in  shade.  Plants  may  receive  too  little  light  by  being 
planted  so  closely  together  that  they  shade  one  another,  or 
where  a  subsequent  growth  of  weeds  springs  up  and  over- 
shadows them.  Fruit  trees  and  flowering  plants,  generally, 
may  fail  to  form  flower  buds  unless  pruned  sufficiently  to  let 
the  light  into  the  mass  of  foliage.  A  large  number  of  woody 
plants  have  the  faculty  of  self-pruning.  This  is  regarded  as 
a  response  to  insufficient  light.  The  cottonwood  is  one  of  the 
best-known  trees  with  this  habit.  In  winter  the  earth  beneath 
old  trees  is  thickly  strewn  with  twigs  a  foot  or  more  long,  cut 
off  by  the  tree  as  smoothly  as  the  leaves  are.    ■ 


TEMPERATURE,  LIGHT,  AND  MOISTURE       123 


Blanching.  Plant  parts  produced  in  darkness  are  paler  and 
tenderer  than  when  grown  in  the  light,  and  this  fact  gives 
reason  for  the  process  known  as  blanching.  Plants  may  be 
blanched  by  heaping  up  the  soil  about  them,  or  by  covering 
them  with  boards,  tiles,  or  anything  else  that  will  exclude 
light.  Celery  and  sea  kale  are  always  blanched  for  the  table 
in  this  way,  and  asparagus  often  is.  Endive  is  blanched  by 
tying  the  outer  leaves 
over  the  center  a  few 
weeks  before  using,  and 
by  the  same  method 
the  heads  of  cauliflower 
are  protected  from  the 
light  and  kept  white. 

Protection  from  light. 
Light  and  heat  are  so 
closely  allied  that  what 
will  protect  from  one 
will  usually  protect 
from  the  other.  The 
lath  house,  built  of  com- 
mon lath  or  of  wider 
strips  separated  from 
one  another  by  suffi- 
cient space  to  admit 
some  of   the   light,   is 

often  used  for  growing  shade  plants,  slow-growing  seedlings, 
and  similar  specimens.  In  addition  to  this  protection  from 
light  and  the  attendant  heat,  the  lath  house  retains  the 
moisture  in  the  air.  Artificial  shading  by  means  of  thin  cloth 
or  lath  screens  is  frequently  employed  in  the  cultivation  of 
tobacco,  coffee,  pineapples,  and  ginseng.  In  summer  radishes 
and  lettuce  come  to  much  greater  perfection  when  grown  in 
the  shade. 


I'lioto^rapli  by  the  University  of  Illinois 

Fig.  88.    Cauliflower  plant 
The  leaves  are  tied  above  to  blanch  the  center 


124  AGRONOMY 

Effects  of  overwatering.  Although  plants  need  much  mois- 
ture, they  may  very  easily  have  too  much,  which  results  in 
various  abnormal  conditions.  Tomatoes,  cabbage,  melons, 
plums,  and  other  fruits  are  liable  to  crack  from  this  cause, 
when  heavy  rains  follow  a  drought.  Anything  that  will  cause 
a  reduction  in  the  water  supply  may  act  as  a  remedy.  In  the 
case  of  cabbage,  pulling  on  the  stem  so  as  to  break  some  of 
the  roots  may  prevent  the  heads  from  bursting.  House  plants 
are  frequently  overwatered.  Few  plants  can  long  keep  up  the 
struggle  if  left  standing  in  a  jardiniere  containing  an  inch  or 
more  of  water. 

Time  to  water.  Air  in  the  soil  is  a  necessity.  A  saturated 
soil  is  as  harmful  as  one  that  is  too  dry.  About  50  or  60  per 
cent  of  the  moisture  a  soil  can  hold  is  about  the  amount  de- 
sirable. When  watering  plants  it  is  better  to  give  the  ground 
a  good  soaking  at  considerable  intervals  than  to  give  it  more 
frequent  applications  of  smaller  amounts.  Light  watering 
makes  plants  shallow  rooted  and  more  susceptible  in  times  of 
drought.  A  few  plants,  such  as  the  geranium,  petunia,  and 
tomato,  possess  glandular  hairs  which  have  the  faculty  of  ab- 
sorbing moisture  from  the  air  or  from  dew.  This  accounts  for 
their  ability  to  thrive  in  places  too  dry  for  ordinary  plants. 
The  so-called  "  Spanish  moss  "  of  the  Southern  states,  which  is 
really  a  relative  of  the  pineapple,  absorbs  all  its  moisture 
through  its  leaves. 

Effects  of  lack  of  water.  Plants  grown  without  an  adequate 
supply  of  water  are  inclmed  to  be  short  and  stunted,  but  the 
lack  of  moisture  favors  the  development  of  flower  buds  and 
causes  the  wood  to  ripen.  A  large  number  of  our  spring 
flowering  plants  form  their  flower  buds  during  the  heat  and 
drought  of  summer,  and  florists  allow  their  plants  to  become 
pot-bound  when  flowers  are  desired,  since  this  prevents  the 
absorption  of  much  water  and  food  materials.  Removing  part 
of  the  root  system  may  have  the  same  effect. 


TEMPERATURE,  LIGHT,  AND  MOISTURE       125 


Water  and  plant  forms.  Although  the  character  of  the  soil 
determines  in  great  measure  the  kind  of  plants  that  will  thrive 
in  it,  and  temperature  may  have  much  to  do  m  determining 
their  distribution,  water  is  of  still  greater  importance,  since  it 
affects  both  the  form  and  structure  of  vegetation.  The  plants 
of  the  world  may  be  separated  into  three  ecological  groups, 
known  as  xerophytes,  hydrophytes,  and  mesophytes,  accord- 
ing to  the  amount  of  water  to  which  they  are  adjusted.  The 
xerophytes,  or  drought  plants,  can 
thrive  with  a  very  limited  sup- 
ply of  moisture.  They  inhabit 
deserts  and  other  dry  locali- 
ties and  are  characterized  by 
many  adaptations  for  conserv- 
ing moisture,  such  as  condensed 
stems,  reduced  leaf  surface, 
thick  epidermis,  an  extensive 
root  system,  and  various  tis- 
sues for  water  storage.  Many 
xerophytes  are  leafless  and  the 
stems  perform  the  work  of  pho- 
tosynthesis, others  have  leaves 
for  a  part  of  the  year  but  drop 
them  when  seasons  of  drought  occur.  In  the  species  which 
retain  their  leaves,  the  latter  are  usually  covered  with  hairs, 
scales,  or  bloom.  Xerophytes  often  have  their  stems  under- 
ground in  the  form  of  rootstocks,  bulbs,  and  corms,  and  the 
production  of  thorns  and  spines  by  woody  species  is  common. 
The  cactus,  yucca,  and  houseleek  are  xerophytes.  All  xero- 
phytes do  not  live  in  deserts,  however.  A  rocky  ledge  or  a 
sand  dune,  though  located  in  a  region  of  abundant  rainfall, 
may  hold  so  little  moisture  that  the  plants  that  grow  upon 
them  are  exposed  to  desert  conditions  and  may  have  all  the 
characteristics  of  drought  plants.  The  lichens  which  grow  upon 


Pig.    89.    Yucca   glauca,    a    xero- 
phyte  of  the  Western  plains 


126 


AGRONOMY 


Fig.  90.   Tree  yuccas,  xerophytic  plants  of  the  Mohave  Desert 

the  trunks  of  trees,  rocks,  and  in  similar  places  are  examples 
of  such  plants.  Hydrophytes  are  water  plants  and  thrive  only 
in  regions  of  abundant  rainfall.  The  water  lily,  pickerel  weed, 
ditch  moss,  and  pondweed  are  good  illustrations.    They  are 


Fig.  91.    The  American  lotus  {NeLumbo),  a  hydrophyte 


TEMPEKATURE,  LIGHT,  AND  MOISTURE       127 

characterized  by  weak  stems,  thin  epidermis,  few  roots,  Httle 
conducting  tissue,  and  large  air  spaces  withhi  stems  and  leaves, 
all  of  which  are  necessary  to  fit  them  to  their  envuonment. 
The  leaves  under  water  are  usually  narrow  or  much  branched, 
though  those  exposed  to  the  air  may  be  as  large  as,  or  larger 
than,  in  other  plants.  Along  with  the  true  hydrophytes  are 
often  found  other  plants  that  are  xerophytic  in  structure, 
though  growing  m  water.    These  are  sometimes  known  as 


A  group  of  hydrophytes,  showing  the  zonation  that  often  occurs 


In  the  water,  spatter-dock  {X^>phar)  and  algae ;  on  the  muddy  shore,  a  belt  of  cat- 
tails ;  in  the  background,  cottonwoods  and  willows 

xerophytic  hydrophytes.  They  are,  for  the  most  part,  plants 
which  absorb  so  slowly  that  they  have  been  obliged  to  adopt 
the  structure  of  xerophytes  in  order  to  retain  what  mois- 
ture they  absorb.  The  scouring  rush  illustrates  plants  of  this 
type.  The  mesophytes  occupy  the  middle  ground  between  the 
xerophytes  and  hydrophytes.  They  are  the  common  plants 
of  bur  woods  and  fields,  and  though  of  far  more  economic 
importance  than  either  of  the  other  classes,  they  are  of  much 
less  botanical  interest. 


128  AGRONOMY 

PRACTICAL  EXERCISES 

1.  Visit  the  nearest  hothouse  and  note  the  character  of  the  tropical 
perennials  that  require  great  heat  for  growth. 

2.  Ascertain  from  the  nearest  weather  observer,  or  from  farmers  who 
have  kept  records,  the  average  date  of  the  last  killing  frost  in  spring 
and  the  earliest  killing  frost  in  autumn.  How  many  days  of  growing 
weather  does  this  give  you  ?  Find  the  date  of  the  latest  recorded  spring 
frost  and  the  date  of  the  earliest  autumn  frost.  How  many  days  from 
frost  to  frost  ?  How  does  this  compare  with  the  average  ? 

3.  Into  a  bright  tin  cup,  nearly  filled  with  water,  drop  pieces  of  ice 
one  by  one,  stirring  the  mixture  with  a  thermometer.  When  moisture 
begins  to  appear  on  the  outside  of  the  tin  cup,  the  thermometer  will 
register  the  dew  point.  Where  is  the  dew  point  higher,  in  the  school- 
room or  in  a  sheltei-ed  place  outside  ?  In  which  place  does  the  air  hold 
the  more  moisture  ? 

4.  Find  a  place  where  a  board,  paper,  or  other  object  has  been  lying 
on  the  grass  for  a  few  days.  Remove  it  and  account  for  the  appearance 
of  the  grass  underneath. 

5.  Examine  potatoes  or  other  plants  that  have  grown  in  a  cellar  or 
other  dark  place.    Explain  the  appearance  of  the  plants. 

6.  Make  lath  screens  for  use  in  the  garden  later,  or  draw  plans  to 
scale  for  a  lath  house  to  be  constructed  in  the  garden  for  growing  the 
shade  plants. 

References 

Dryer,  "'Les.sons  in  Physical  Geography." 
Goff,  "Principles  of  Plant  Culture." 
Salisbury,  "  Physiography." 

Farmers^  Bulletin 

104.  Notes  on  Frost. 

Weather  Bureau 

311.  Climate  ;  its  Physical  Basis  and  Controlling  Factors. 


CHAPTER   IX 

GARDEN   MAKING 

Location  of  the  garden.  The  ideal  location  for  a  garden  is 
in  a  well-drained  spot,  open  to  the  south  and  east,  and  pro- 
tected at  least  on  the  north  by  a  belt  of  evergreen  trees,  a 
high  wall,  or  a  tight  board  fence,  but  any  place  is  suitable  if 
it  receives  the  direct  rays  of  the  sun  for  at  least  half  of  the 


Fig.  93.   A  class  at  work  on  a  city  lot,  Joliet,  Illinois 

day.  Land  sloping  toward  the  north  should  be  avoided  and 
so  should  a  locality  where  there  is  much  smoke.  In  the 
majority  of  cases,  however,  it  is  not  possible  to  select  a  new 
site  for  the  garden,  and  one's  efforts  must  be  directed  toward 
bettering  the  one  he  already  possesses.    The  nearer  it  can  be 

129 


130  AGRONOMY 

made  to  approach  ideal  conditions  the  better.  If  the  garden 
is  to  contain  fruit  trees,  these  should  be  placed  along  the 
north  line  or  otherwise  disposed  so  that  they  will  not  shade 
the  growing  crops. 

Preparing  the  soil.  The  best  soil  is  a  deep  and  moderately 
light  loam,  but  here,  again,  one  must  make  the  best  of  his 
situation.  Large  stones  should  be  removed,  but  small  ones 
may  remain.  Gravelly  soils  are  early  soils  because  during  the 
day  the  stones  absorb  much  heat  which  they  radiate  at  night. 
If  the  soil  is  a  stiff  clay,  it  may  be  lightened  by  the  addition 
of  sand,  coal  ashes,  lime,  stable  manure,  dead  leaves,  and  other 
litter.  Sandy  soils  may  be  improved  by  digging  uito  them 
anything  that  will  add  humus,  and  any  soil  will  be  benefited 
by  the  application  of  well-rotted  manure.  The  soil  should  be 
made  mellow  by  plowing  or  deep  spading,  all  lumps  should 
be  broken  up  with  the  rake  or  hoe,  and  the  surface  finally 
leveled  with  a  rake.  The  care  with  which  the  seed  bed  is 
made  will  be  reflected  in  the  crops.  It  is  not  economy  to 
plant  until  the  soil  has  been  properly  prepared. 

The  garden  plan.  Before  planting,  a  plan  of  the  garden 
drawn  to  scale  should  be  made.  In  this  plan  all  paths  and 
permanent  crops  and  the  area  devoted  to  each  vegetable 
should  be  indicated.  By  this  means  one  can  discover  in 
advance  exactly  how  many  plants  he  will  have  room  for,  and 
can  plant  any  part  of  his  space  without  encroaching  upon 
that  reserved  for  other  things.  Permanent  plants,  such  as 
raspberries,  currants,  asparagus,  and  rhubarb,  should  be  re- 
stricted to  the  borders  where  they  will  not  interfere  with  the 
cultivation  of  the  other  crops  year  after  year.  ]\Iany  paths 
should  be  avoided,  but  those  that  are  maintained  should  enable 
one  to  reach  all  parts  of  the  garden  expeditiously  and  should 
be  wide  enough  to  permit  of  being  traversed  with  a  wheel- 
barrow. It  is  no  longer  the  custom  to  plant  the  smaller 
vegetables  in  narrow  beds.    They  should  be  planted  in  rows, 


CtlEKAXTS 


KlUUtARB 


ASPAKAGl'S 


-Pf.tiennial- 


OxiONS  -  2  rows 


-Parsnips- 
— 4-ro'ws — 


-Carrots- 
— 3  rows — 


-Salsify- 
— 3  rows— 


-Kohl  Kaiu- 

3  rows 

Peas 


-3  double  rows- 


-^ Beets- 

-^  —  2  rows  - 

w 


; — SriNAcii — 

I 3  rows 

I 

-Onion  Sets- 
2  rows 


-Radishes- 
— 2  rows — 


-Lettcce- 
2  rows 


131 


-CORN- 


-witb- 


-TURNIPS   or- 

— Squash — 


-Pole  Beans- 
3  rows 


-TOMATOES- 

— 4  rows — 


-Bush  Beans- 
3  rows 


10  ft. 


132 


AGRONOMY 


the  longer  the  better,  to  permit  of  the  ground  being  worked 
more  easily.  Care  must  be  taken,  however,  to  so  arrange  the 
planting  with  reference  to  the  points  of  the  compass  that  tall 
growing  plants  are  not  placed  where  they  will  shade  lower 
ones.  In  general,  it  is  well  to  place  nearest  the  house  the 
salad  plants  and  others  that  are  gathered  frequently,  leaving 
the  field  crops,  like  potatoes  and  cabbage,  to  occupy  more 
distant  spots. 

How  to  plant.   A  few  plants,   such  as   com,   cucumbers, 
tomatoes,  and  pole  beans,  are  planted  in  lulls,  but  all  that,can 


Fig.  95.   Gardening  at  the  Flower  Technical  High  School  for  Girls,  Chicago 

be  grown  in  drills  or  rows  are  so  planted  to  facilitate  culti- 
vation. Care  should  be  taken  to  have  the  rows  straight  and 
far  enough  apart  to  avoid  crowding.  The  proper  distances 
may  be  learned  by  consulting  the  planting  table  on  page  145. 
To  facilitate  measurements  in  the  garden,  the  handle  of  hoe  or 
rake  should  be  laid  off  in  six -inch  sections.  The  marks  can  be 
scratched  in  the  wood  with  any  sharp-pointed  instrument  and 
inked,  if  desired.  Straight  rows  may  be  secured  by  means  of  a 
garden  line,  such  as  masons  use,  stretched  between  two  stakes. 


w  / 
m  / 

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Experiments           | 

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i7a;p'<s     \Exp'ts 

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Lawn          /^ 

Fig.  96.   Four  plans  for  school  gardens  on  vacant  lots 
188 


134  AGRONOMY 

When  not  in  use  it  should  be  kept  with  the  seeds  where  it 
will  be  ready  when  more  planting  is  to  be  done.  Seeds  must 
not  be  planted  too  deep.  In  general  they  should  be  planted 
three  or  four  times  as  deep  as  their  diameters.  Seeds  whose 
cotyledons  do  not  rise  above  the  soil  may  be  planted  deeper 
than  those  whose  cotyledons  do,  and  large  seeds  may  be  planted 
deeper  than  smaller  ones.  Very  small  seeds  may  be  simply 
scattered  on  the  surface  and  pressed  into  the  soil  with  a  hoe 
or  a  piece  of  board.  When  sown  in  light,  well-drained  soil, 
the  seeds  may  have  the  earth  firmed  over  them  to  induce 
capillarity,  but  in  wet  or  heavy  soils  this  should  be  omitted, 
else  it  may  be  so  compacted  that  delicate  plants  cannot  push 
through  it  and  the  air  necessary  for  germination  be  excluded. 
Darkness  favors  the  germmation  of  most  seeds,  and  for  this 
reason,  as  well  as  to  prevent  the  drymg  out  or  puddling  of 
the  surface  layer  of  soil,  it  is  well  to  mulch  newly  planted 
seeds  with  a  light  covering  of  loose  straw  or  lawn  clippings 
through  which  the  young  plants  easily  push  their  way.  Cover- 
ing the  planted  seeds  with  paper  or  cloth  serves  the  same  pur- 
pose, but  in  such  cases  the  cover  should  be  removed  as  soon 
as  the  young  plants  appear. 

When  to  plant.  The  seeds  of  the  hardier  plants  may  be 
sown  as  soon  as  the  ground  can  be  worked  in  spring,  or  they 
may  even  be  sown  in  the  autumn  and  allowed  to  rest  in  the 
soil  through  the  winter.  This  is  the  way  all  the  wild  species 
are  planted.  Other  seeds  must  not  be  planted  until  the  soil  is 
thoroughly  warmed.  Several  garden  plants  thrive  only  in  the 
cool  moist  days  of  early  spring,  and  do  not  grow  well  if 
planted  later.  This  is  especially  true  of  spinach,  cress,  radishes, 
lettuce,  and  the  like.  In  hot  dry  weather  these  plants  soon 
"  run  to  seed."  Among  the  vegetables  that  are  usually  planted 
early  are  beets,  cabbage,  cress,  lettuce,  onions,  peas,  radishes, 
salsify,  and  spinach.  These  are  either  cool-season  or  long-sea- 
son plants  that  are  not  injured  by  light  frosts.   Warm-season 


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135 


136  AGRONOMY 

plants,  such  as  corn,  cucumbers,  okra,  peppers,  and  tomatoes, 
must  not  be  planted  outdoors  until  all  danger  from  frost 
is  past. 

Autumn  seed  bed.  The  seeds  of  all  hardy  plants  may  be 
sown  in  autumn  and  will  lie  in  the  earth  unharmed  until 
spring.  Some  will  even  grow  in  autumn  and  go  through  the 
cold  season  as  seedlmgs.  Autumn  seed  sowing  has  the  ad- 
vantage that  it  may  be  done  at  a  time  when  other  work  is  not 
crowding,  as  in  spring,  and  the  stay  in  the  soil  over  winter 
will  aid  in  softening  the  seed  coats  of  many  species.  In 
autumn,  also,  fruitmg  plants  are  everywhere  and  seeds  are 
abundant.  It  is  much  easier  to  carry  home  a  dozen  plants  as 
seeds  than  to  transport  the  same  number  when  they  have 
grown  for  a  year  or  more.  The  autumn  seed  bed  should  be 
made  in  a  sheltered  situation,  and  when  cold  weather  has 
come,  it  should  be  mulched  with  some  good  litter  that  is 
free  from  weed  seeds. 

Germination.  The  promptness  with  which  the  young  plants 
appear  above  the  soil  depends  upon  the  kind  of  seed  planted, 
the  temperature  of  the  soil,  the  amount  of  moisture  present, 
and  various  other  things.  In  cold,  wet  soils  seeds  of  most  sorts 
are  slow  to  germinate,  if  they  grow  at  all,  though  a  few  will 
sprout  at  temperatures  but  slightly  above  freezmg.  Increas- 
ing the  temperature,  however,  hastens  germination,  and  in 
dry  weather  soaking  the  seeds  before  planting  has  the  same 
effect.  Hardy  plants  usually  do  best  at  temperatures  of  from 
50°  to  70°,  tender  plants  from  60°  to  80°,  and  tropical  plants 
from  75°  to  95°.  In  favorable  weather  from  tlu-ee  days  to  two 
weeks  may  elapse  between  planting  and  the  appearance  of 
the  seedlings.  Seeds  of  canna,  lotus,  honey  locust,  and  some 
others  have  testas  so  hard  that  they  delay  germination  by  ex- 
cluding moisture  and  air,  but  they  grow  readily  when  a  hole  is 
filed  tlu-ough  the  testa  before  planting.  Boiling  water  is  some- 
times poured  over  such  seeds  to  hasten  germination.    The 


GARDEN  MAKING 


137 


seeds  of  nut  trees  and  our  stone  fruits  have  testas  so  thick 
that  they  may  remain  in  the  earth  for  a  year  or  more  before 
growing.  In  such  cases  germination  may  be  hastened  by 
cracking  the  shells  or  by  stratifying  the  seeds.  The  latter 
process  consists  in  plac- 
ing the  seeds  in  layers 
in  boxes  of  moist  sand 
or  moss  and  keeping 
them  moist  during  the 
winter.  The  seeds  may 
be  kept  in  a  cool  cel- 
lar or  buried  a  foot  or 
more  deep  in  a  well- 
drained  spot.  Seeds 
may  fail  to  grow  for 
various  reasons.  They 
may  be  too  old,  may 
have  been  frozen  before 
being  thoroughly  dried, 
their  testas  may  exclude 
oxygen  or  moisture,  or 
they  may  hate  been 
immature  when  gath- 
ered. The  seeds  of 
many  plants  will  not 
grow  the  same  season 
they  are  produced,  even 
if  surrounded  by  the 
most  favorable  circum- 
stances. The  length  of 
time  that  good  seeds  retain  their  vitality  depends  somewhat 
upon  the  species.  A  few  seeds  must  be  planted  almost  as  soon 
as  ripe  if  they  are  to  grow  at  all,  while  others  will  remain  alive 
for  from  two  to  twenty  years.   In  general,  starchy  seeds  retain 


Fig.  98. 


AhandyreceptiiLk  im  .^ 
and  other  small  things 


uud.-.,  labuLs, 


This  is  easily  made  and  can  be  carried  into  the 
garden  whenever  planting  is  to  be  done 


138  AGRONOMY 

their  vitality  longer  than  oily  ones.  There  is  no  truth,  how- 
ever, in  the  idea  that  seeds  thousands  of  years  old,  found  in 
the  pyramids  or  dug  out  of  Indian  graves,  will  grow.  Weed 
seeds  are  especially  persistent,  but  few  of  them  can  grow  after 
twenty  years.  In  some  seeds  the  age  seems  to  affect  the  crop, 
fresh  seeds  producing  more  vigorous  plants  witli  a  tendency 
to  put  forth  leaves  and  stems  only,  while  older  ones  are  likely 
to  be  more  fruitful.  Growers  of  melons  prefer  seeds  several 
years  old  for  this  reason. 

Seed  testing.  When  a  crop  is  planted  upon  which  much 
depends,  or  when  for  any  reason  there  is  doubt  about  the  seeds 
bemg  good,  it  is  customary  to  test  them  before  planting.    A 


A  B 


Ttffi.  9d.  A  seed  tester,  consisting  of  two  soup  plates,  some  sand,  and  a 
i?  piece  of  cloth 

I 

serviceable  seed  tester  may  be  made  of  a  dinner  plate,  a  sheet 
of  glass,  and  two  pieces  of  rather  thick  cloth  cut  to  fit  the  plate. 
The  clotlis  are  dipped  in  water,  the  excess  moisture  wrung 
out,  and  the  seeds  to  be  germinated  placed  between  them. 
The  cloths  are  placed  on  the  plate  and  covered  with  the  glass 
or  another  plate  to  keep  in  the  moisture,  and  the  apparatus 
set  away  in  a  warm  place.  From  time  to  time  the  seeds  are 
examined  and  those  which  have  germinated  removed.  By  this 
means  one  may  very  quickly  discover  what  proportion  of  a 
given  lot  of  seeds  is  viable.  Wet  sand  may  be  used  in  place 
of  the  cloth  in  the  seed  tester,  if  desired. 

Double  cropping.  Different  crops  vary  greatly  in  the  time 
taken  to  mature.  Long-season  crops,  such  as  salsify  and  pars- 
nips, are  planted  early  in  spring,  occupy  the  ground  until  frost, 


GARDEN  MAKING 


139 


and  are  often  left  in  the  soil  over  winter.  On  the  other  hand, 
lettuce,  radishes,  and  the  like  take  but  a  few  weeks  to  mature, 
and  if  such  crops  are  planted  together  in  one  part  of  the  gar- 
den, two  and  three  separate  crops  may  be  grown  on  the  same 
soil  hi  one  season.  Among  the  plants  most  useful  for  second 
crops  are  beans,  cress,  celery,  cabbages,  kohl-rabi,  lettuce, 
mustard,  radishes,  spinach, 
and  turnips.  Celery  and 
cabbages  used  as  late  crops 
are  started  elsewhere  and 
transplanted  ;  the  others  are 
grown  from  seeds  planted 
where  they  are  to  remain. 
Another  method  of  get- 
ting two  crops  from  the 
same  soil,  often  practiced 
with  long-season  crops,  is 
to  plant  together  two  crops, 
each  of  which  has  different 
requirements  as  to  light, 
shade,  etc.  Pumpkins,  tur- 
nips, and  squashes  are  often 
planted  with  corn,  and  clover 
with  grain  crops.  Radishes 
may  be  planted  with  salsify, 
beets,  and  other  slow-grow- 
mg  crops,  and  help  to  mark 

the  rows  until  the  other  plants  have  developed.  Radishes 
and  lettuce  may  also  be  planted  between  the  hills  in  melon 
patches,  where  they  will  mature  before  the  space  is  needed 
by  the  chief  crop. 

Transplanting.  Almost  any  plant  can  be  transplanted,  but 
some  endure  such  treatment  better  than  others.  Plants  with 
strong  taproots  are  more  difficult  to  transplant.    In  general, 


Fig.  100.   A  garden  plan  which  may  be 

used  for  a  school   garden   or   for   the 

home  lot 


140 


AGRONOMY 


when  directions  on  a  seed  packet  say  the  seeds  should  be 
sown  where  the  plants  are  wanted,  transplanting  should  not 
be  attempted.  There  are  several  advantages,  however,  to  be 
gained  by  transplanting.  Earlier  crops  may  be  produced  by 
starting  plants  in  the  house  before  they  can  grow  out  of  doors, 
and  transplanting  them  to  the  garden  when  the  weather  has 
moderated.    Plants  that  require  a  long   season  to   come  to 

maturity  may  also  be  in- 
duced to  fruit  earlier  by 
this  means.  By  starting 
plants  in  this  way  they 
may  be  set  in  the  place  of 
those  that  mature  early 
and  a  second  crop  thus 
secured,  or  they  may  be 
used  to  fill  up  gaps  in 
the  plantings  caused  by 
the  depredations  of  in- 
sects, plant  diseases,  or 
the  failure  of  the  seeds 
to  grow.  Warm-season 
plants  are  usually  long- 
season  plants  also,  and 
several  of  these,  such  as 
eggplants,  peppers,  and  tomatoes,  are  always  transplanted, 
thus  securing  earlier  and  more  abundant  crops.  Other  plants 
that  are  able  to  mature  from  seed  planted  in  the  open  ground 
are  usually  treated  in  this  way,  especially  cabbage,  cauliflower, 
and  celery.  Beets,  chard,  lettuce,  and  onions  are  occasionally 
transplanted. 

Transplanting  should  be  done  on  cool  or  cloudy  days  and 
preferably  in  the  late  afternoon.  Young  plants  may  be  trans- 
planted as  soon  as  they  have  developed  their  second  or  third 
leaves.     Moving  very  young   plants    in   this  way  is  called 


Fig.  101.    A  transplanting  trowel  and  a 

dibber 
A  trowel  of  this  kind  is  often  used  as  a  dibber 


GARDEN  MAKING  141 

pricking  out.  The  plants  should  be  taken  up  with  as  many  of 
the  roots  as  possible,  and  should  not  be  allowed  to  become  dry 
by  exposure  to  the  sun  and  air.  The  holes  m  which  they  are 
planted  may  be  made  with  a  pointed  instrument  of  wood  or 
metal  called  a  dibber.  After  the  plants  are  placed  in  the  holes 
the  dibber  is  again  thrust  into  the  ground  an  inch  or  more 
from  them  and  used  to  crowd  the  soil  against  them,  thus  mak- 
ing it  firm.  If  the  weather  is  very  dry,  the  plants  should  be 
watered  after  setting,  and  protected  from  the  wind  and  the 
direct  rays  of  the  sun  until  again  estab- 
lished. Excessive  transpiration  may  be 
reduced  or  avoided  by  removing  some  of 
the  leaves  or  by  cutting  off  part  of  each 
leaf.  The  latter  operation  is  called  shearing. 
Some  growers  are  m  the  "habit  of  allowing 
cabbage  and  tomato  plants  to  wilt  before     F^«- 102.  A  sheared 

r  .,1.1,         ,  1    .  plant 

resettmg,  with  the  idea  that  by  so  doing 

the  plants  will  develop  new  roots  instead  of  endeavoring  to 
revive  the  old  ones.  These  species  are  quite  tenacious  of  life 
and  survive  much  abuse.  Frequently  cabbage  plants  for 
transplanting  are  simply  pulled  up  from  the  seed  bed. 

Inducing  plants  to  fruit.  It  is  natural  that  all  mature  peren- 
nial plants  should  flower  and  fruit  annually,  but  it  is  a  well- 
known  fact  that  many  do  not  do  so.  Fruiting  is  a  very 
exhausting  process.  Annuals  are  killed  outright  by  it,  while 
in  perennials  a  heavy  crop  of  fruit  may  so  depress  the  vitality 
of  the  plant  as  to  make  it  impossible  for  it  to  bear  at  all  the 
following  season.  When  a  plant  sets  more  fruits  than  it  should 
bear,  some  of  them  should  be  removed.  On  the  other  hand,  in 
all  plants  in  which  great  development  of  the  vegetative  parts 
is  desired,  it  is  customary  to  remove  all  the  flowering  shoots 
and  fruits  as  soon  as  they  appear.  Thus  we  pick  off  the  berries 
of  asparagus  and  pinch  out  the  flower  stalks  of  rhubarb. 
Annuals  may  be  made  to  take  on  a  perennial  character  by 


142  AGRONOMY 

removing  the  flower  buds  as  fast  as  they  form.  If  one  desu-es 
flowers  and  fruit,  however,  all  efforts  should  be  bent  toward 
aiding  the  plant  to  store  up  reserve  food,  since  the  more  food 
it  has,  the  likelier  it  is  to  bloom.  Fruiting  is  really  a  device 
of  the  plant  for  self-preservation,  and  whatever  threatens  the 
growth  processes  may  serve  to  bring  it  about.  A  plant  injured 
by  lightning  or  defoliated  by  insects  is  likely  to  spring  into 
bloom  agaui  even  in  autumn.  Pinching  back  the  tips,  remov- 
ing some  of  the  roots,  withholding  water,  or  planting  in  sterile 
soil  will  usually  induce  the  plant  to  fruit.  Certain  varieties 
of  strawberries,  pears,  apples,  plums,  and  other  plants  are  often 
infertile  when  pollinated  with  pollen  from  their  own  flowers. 
Even  when  planted  in  groups  they  may  produce  abundant 
bloom  but  set  little  fruit.  The  remedy  here  is  to  plant  among 
them  other  varieties  with  effective  pollen.  In  a  few  other  forms 
the  pistils  and  stamens  are  produced  on  separate  individuals, 
and  no  fruits  can  be  produced,  therefore,  if  the  pollen-bearing 
plant  is  absent.  Still  other  plants  are  adapted  to  cross-pollination 
by  insects,  and  though  the  pollen-bearing  plant  or  flower  may 
be  present,  they  set  no  fruits  if  the  necessary  insect  fails  to 
visit  them.  In  growing  melons,  cucumbers,  tomatoes,  and 
the  like  in  the  hothouse,  in  winter,  pollination  must  be  per- 
formed by  hand.  Morning  is  the  best  time  for  this  work.  A 
soft  camel's-hair  brush,  to  which  the  pollen  adheres,  may  be 
used  for  the  transfer  of  the  pollen,  or  a  stick  of  sealing  wax 
which  has  been  electrified  by  rubbing  with  a  cloth  may  be 
used  to  pick  up  the  pollen  grains  and  drop  them  upon  the 
stigmas  of  the  flowers  to  be  pollinated. 

Thinning.  When  the  young  plants  are  well  up,  it  will  be 
necessary  to  thin  them,  if  planted  very  thickly.  Thinnmg 
should  be  done  as  early  as  the  plants  can  be  conveniently 
handled,  so  that  the  specimens  left  may  have  room  to  develop 
naturally.  Plants  that  are  not  thinned  become  drawn  and 
spindling  and  do  not  produce  good  crops.    The  distance  apart 


GAEDEN  MAKING 


143 


in  the  row  depends  somewhat  upon  the  habit  of  the  plant. 
Plants  with  long  narrow  leaves,  like  salsify  or  onion,  may  stand 
closer  than  those  with  broad,  spreading 
leaves,  like  turnip  and  parsnip.  The  main 
consideration  should  be  to  see  that  one 
plant  does  not  unduly  shade  another. 

Labels.  All  planted  seeds  should  be  prop- 
erly labeled,  partly  as  a  matter  of  record  and 
partly  to  indicate  their  whereabouts  until 
the  young  plants  are  large  enough  to  be 
seen.  Older  plants  should  also  be  labeled, 
especially  if  there  are  several  varieties  of 
the  same  species  cultivated,  or  if  other 
plants  are  grown  that  might  be  mistaken 
for  them.  The  best  label  for  temporary 
purposes  is  a  wooden  stake  painted  white. 
Such  labels  can  be  purchased  from  seeds- 
men at  small  cost.  Those  six  inches  long 
and  about  three  quarters  of  an  inch  wide 
are  about  the  right  size,  though  smaller  or 
larger  ones  may  be  had.  On  a  label  of  this 
kind,  words  written  with  a  pencil  will  be 
legible  for  years,  though  splashed  with  dirt 
by  every  passing  storm.  For  more  perma- 
nent labels,  however,  it  is  desirable  to  use  a 
piece  of  galvanized-iron  wire  about  fifteen 
inches  long  with  a  coil  at  the  upper  end  to 
which  a  small  label  is  attached.  These  small 
labels,  called  tree  labels,  may  be  obtained  at 
slight  expense.  When  more  than  one  word 
is  to  go  on  a  label,  the  first  word  is  written 
near  the  top  and  lengthwise  of  it,  and  the  second  word  is  written 
under  the  first  and  further  from  the  top.  This  insures  that,  as 
the  label  becomes  less  legible  in  course  of  time,  there  will  be  no 


Fig.  103.   Two  forms 
of  labels 

The  one  on  the  right  is 
the  common  garden  or 
pot  label ;  the  other  is 
a  more  permanent  form 
for  marking  plants  in 
the  borders 


144 


AGROKOMY 


^S 


ai/a.A  eaet- 


Fk;.  104.    Proper  niL'tlKul  of  writing  labels 


chance  of  confusing  the  two  words  in  deciphering  them.  Labels 
should  be  so  placed  as  to  stand  at  the  beginning  of  tlie  rows 
with  the  writing  facing  away  from  the  seeds  or  plants  they  refer 

to.  Unless  this 
rule  is  consist- 
ently followed, 
when     several 

kinds  are  planted  m  the  same  row,  there  is  no  way  of  discover- 
ing on  which  side  of  the  label  the  plants  are  that  bear  the  name. 
Saving  seed.  In  many  cases  it  is  as  well  to  save  the  seeds 
of  desirable  crops  as  it  is  to  buy  new  supplies  of  the  seedsman 
annually.  For  the  purpose  of  seed  production  one  should 
select  the  best  specimens  and  take  care  that  inferior  stock 
does  not  become  mixed  with  it,  through  cross-pollination.  By 
careful  selection  one  may  produce  even  better  crops  than  the 
original.  It  is  not 
desirable,  however, 
to  save  the  seeds  of 
double  flowers  or 
of  plants  that  grow 
near  other  varieties 
of  the  same  species, 
because  they  are  not 
likely  to  come  true 
from  seed  the  fol- 
lowing year.  The 
different  varieties  of 
corn  readily  mix  in 
this  way,  and  so  do  plants  that  produce  flowers  of  several  dif- 
ferent colors.  Seeds  should  be  spread  out  to  dry  in  a  shady 
place,  and  when  thoroughly  dried  should  be  stored  in  a  tin 
box  in  a  cool,  dry  place.  In  warm  climates  seeds  are  usually 
short-lived,  and  in  all  regions  they  require  uniform  conditions 
as  regards  temperature  and  moisture. 


Fig.  105.    A  seed-tight  packet  that  may  be  made 
by  simply  folding  a  sheet  of  paper.    See  page  146 


GARDEN  MAKING 
Table  of  Seeds  and  Distances  for  Planting 


145 


Name 


Beans,  bush 
Beans,  pole 
Beets      .     . 
Carrot     .     . 
Chard,  Swiss 
Corn  .     .     . 
Cress       .     . 
Cucumber  . 
Kohl-rabi     . 
Lettuce  . 
Melons   .     . 
Mustard 
Okra       .     . 
Onion  seed 
Parsley  ,     . 
Parsnip  .     . 
Peas  .     .     . 
Potato     .     . 
Radish    .     . 
Salsify    .     . 
Spinach  .     . 
Squash    .     . 
Turnip    .     . 


I 


How 

PLANTED 


drills 

hills 

drills 

drills 

drills 

hills 

drills 

hills 

drills 

drills 

hills 

drills 

drills 

drills 

drills 

drills 

drills 

hills 

drills 

drills 

drills 

hills 

drills 


Amount 


quart 

quart 

ounce 

ounce 

ounce 

quart 

ounce 

ounce 

ounce 

ounce 

ounce 

ounce 

ounce 

ounce 

ounce 

ounce 

quart 

peck 

ounce 

ounce 

ounce 

ounce 

ounce 


Will  seed 


Distances  apart 
OF  Rows 


150  ft. 
125  hills 

50  hills 
100  ft. 

50  ft. 
125  hills 
100  ft. 

60  hills 
200  ft. 
200  ft. 

60  hills 

80  ft. 

50  ft. 
125  ft. 
100  ft. 
250  ft. 
150  ft. 
100  hills 
125  ft. 

75  ft. 
100  ft. 

25  hills 
150  ft. 


18  in. 

4  ft. 

12  to  18  in. 
12  to  18  in. 
18  to  20  in. 
2^  to  4  ft. 

1  ft. 

4  or  5  ft. 
18  to  24  in. 
12  in. 

5  or  6  ft. 
12  in. 

4  ft. 

1  ft.  or  less 
18  in. 
18  in. 

18  in.  or  more 
21  ft. 
12  in. 
15  in. 
12  in. 

4  to  9  ft. 
12  in. 


Vegetables  usually  Transplanted 


Name 

How 
planted 

Amount 

Will  make 

Distances  apakt 
OF  Rows 

Cabbage      .     .     . 

hills 

ounce 

2000  plants 

2  ft.  or  more 

Cauliflower 

hills 

ounce 

3000  plants 

2  ft.  or  more 

Celery     .     . 

drills 

ounce 

5000  plants 

2  ft. 

Eggplant    . 

hills 

ounce 

2000  plants 

2  ft. 

Onion  sets  . 

drills 

quart 

50  ft. 

12  in. 

Pepper   .     . 

hills 

ounce 

2000  plants 

2  ft. 

Tomato  .     . 

hills 

ounce 

2000  plants 

3  to  4  ft. 

146 


AGRONOMY 


Seed  packets.  In  handling  seeds  a  convenient  packet  in 
which  they  may  be  placed  is  desirable.  The  packet  shown  in 
the  illustration  on  page  144  may  be  made  at  any  time  without 
paste  or  elaborate  manipulation,  and  yet  will  hold  the  smallest 
seeds  securely.  To  make  it,  take  a  sheet  of  paper  of  the  de- 
sired size  —  5  inches  by  7  inches  is  a  convenient  shape  —  and 
fold  it  once  the  long  way  of  the  paper  with  the  two  edges  to- 
gether. Next  fold  back  these  edges  about  a  quarter  of  an  inch 
from  the  edge  and  repeat  the  process.  Then  turning  the  folded 
side  down  with  the  fold  farthest  away,  bend  back  the  corners 


/-. 

f 

Tf:'''^'' 

1 

! 

i 

■''I. 

-i^-M. 

,,:.:. 

/  .-J                          3 

1 

I 

1    ,J 

Fig.  100.    Method  of  closing  the  ordinary  seed  packet 


of  the  folded  side  until  they  meet  the  opposite  edge  and  form 
a  right  angle  with  it.  Next  bend  the  unfolded  corners  down 
and  tuck  the  tips  under  the  first  fold  and  the  packet  is  done. 
When  the  packet  is  to  be  filled  either  end  may  be  quickly 
opened.  When  it  is  desired  to  close  an  ordinary  seed  packet 
such  as  the  seedsmen  use,  fold  one  corner  of  the  open  end  three 
quarters  of  the  way  across,  fold  the  opposite  corner  back  upon 
this,  and  tuck  the  tip  under  the  first  fold.  The  illustrations  will 
aid  in  making  this  matter  clear.  All  packets  of  seeds  should  be 
carefully  labeled  with  the  name  of  the  seeds  within  and  the  date 
at  which  they  were  collected.  It  is  unwise  to  trust  the  mem- 
ory for  data  of  this  kind  which  may  materially  affect  the  crop. 


GARDEN  MAKING  147 

PRACTICAL  EXERCISES 

1.  Carefully  measure  the  school  garden  and  make  a  plan  of  it,  drawn 
to  a  scale  of  ^  or  ^  inch  to  the  foot.    Neatly  label  all  sections. 

2.  How  many  acres.in  the  school  garden  ?  If  less  than  one,  estimate 
the  fraction  of  an  acre.  What  fraction  of  an  acre  is  your  own  jiart  of 
the  school  garden? 

3.  Make  a  plan,  drawn  to  scale,  of  an  average  lot  in  your  town. 
Allow  space  for  house  and  lawns  and  indicate  the  place  in  the  garden 
which  each  vegetable  is  to  occupy. 

4.  Write  to  the  nearest  seedsman  for  a  seed  catalogue,  which  may 
be  had  free,  and  make  a  list  of  the  vegetables  named  in  your  plauj  with 
an  estimate  of  the  quantity  of  seed  needed  for  planting  the  garden. 

5.  Make  out  an  order  for  these  seeds,  with  the  quantities  and  prices, 
and  file  with  your  teacher. 

6.  Write  to  your  representative  in  Congress  for  sufficient  seeds  to 
plant  your  own  garden. 

7.  Get  a  packet  of  any  large  seeds  (radishes,  beans,  or  corn  will  do) 
and  divide  it  into  («)  full  shapely  seeds,  (ft)  irregular  and  small  seeds, 
and  (c)  broken  seeds,  weed  seeds,  and  dirt.  What  percentage  of  the  packet 
is  good  seeds  ? 

8.  Make  a  seed  tester  and  test  twenty  large  seeds  and  twenty  small 
ones  for  vitality.  What  per  cent  of  each  germinated  ?  Which  do  you 
conclude  would  be  best  to  plant  ? 

9.  Plant  your  own  part  of  the  school  garden  and  cultivate  it  after 
every  rain. 

10.  Try  covering  half  a  row  of  planted  seeds  with  a  light  mulch. 
How  does  this  affect  the  germination  of  the  seeds  ?  Compare  with  the 
part  of  the  row  left  uncovered. 

11.  Transplant  lettuce,  beets,  cabbage,  or  other  plants  to  your  garden. 

12.  Select  a  row  of  young  seedlings  planted  rather  thickly,  and  thin 
out  half  the  row  to  the  proper  distances  between  plants  and  allow  the 
other  to  go  untouched.    What  effect  has  crowding  ? 

13.  Fertilize  half  a  row  of  spinach,  lettuce,  or  radishes  with  nitrate 
of  soda,  making  two'  applications  about  a  week  or  ten  days  apart.  How 
does  the  subsequent  growth  compare  with  the  untreated  plants  ? 

14.  Plant  the  seeds  of  desirable  trees  and  shrubs  in  the  school  garden 
where  they  may  grow  into  good  specimens  for  use  on  Arbor  Day.  If 
there  are  small  specimens  already  growing  for  this  purpose,  transplant 


148  AGRONOMY 

them  to  a  new  location  in  order  that  they  may  develop  an  abundance 
of  fibrous  roots. 

15.  Properly  label  all  seeds  as  soon  as  sown.  Make  seed  packets 
according  to  the  directions  given  on  page  146. 

16.  IMake  a  collection  of  vegetable  and  flower  seeds  for  the  school 
museum.  Have  the  specimens  uniform.  Small  bottles  known  as  shell 
vials  are  excellent  containers. 

References 

Bailey,  "Manual  of  Gardening;." 
French,  "The  Book  of  Vegetables." 
Green,  "Vegetable  Gardening." 

Farmers^  Bulletins 

33.  Peach  Growing  for  Market. 

35.  Potato  Culture. 

52.  The  Sugar  Beet. 

61.  Asparagus  Culture. 

76.  Tomato  Growing. 

94.  The  Vegetable  Garden. 
113.  The  Apple,  and  how  to  grow  it. 
121.  Beans,  Peas,  and  Other  Legumes  for  Food. 
148.  Celery  Culture. 
154.  The  Fruit  Garden, 
156.  The  Home  Vineyard. 
161.  Practical  Suggestions  for  Fruit  Growing, 
218.  The  School  Garden. 
235.  Home  Vegetable  Garden, 

Bureau  of  Plant  Industry 

69.  American  Varieties  of  Lettuce. 
109.  American  Varieties  of  Garden  Beans. 
184.  The  Production  of  Vegetable  Seeds. 


CHAPTER   X 

TILLAGE 

Need  for  tillage.  There  are  certain  factors  in  crop  pro- 
duction that  man  can  do  httle  to  change.  The  range  of 
temperature,  the  make-up  of  the  air,  the  amount  and  time 
of  ramfall,  and  the  amount  of  sunhght  are  beyond  his  power 
to  vary ;  but  the  soil,  fully  as  important  as  any  of  these,  may  be 
greatly  modified  by  his  efforts.  By  drainage  he  adds  to  its 
depth  and  warmth,  by  the  addition  of  manures  he  enhances 
its  fertility,  and  by  proper  cultivation  he  promotes  the  develop- 
ment of  the  plants  growing  in  it.  Given  warmth,  moisture,  and 
fertility,  tillage  is  still  necessary  for  the  highest  development 
of  growing  plants.  Even  wild  species  become  more  luxuriant 
and  give  finer  flowers  and  better  flavored  fruits  when  properly 
cultivated.  The  chief  difference  between  our  food  plants  and 
others  of  the  same  kind  growing  wild  is  due  to  the  fact  that  the 
soil  about  the  food  plants  is  tilled.  Tillage  renders  the  soil  less 
compact,  enables  the  roots  of  plants  to  penetrate  it  more  easily, 
adds  to  its  ability  to  absorb  rainfall,  prevents  the  escape  of 
moisture  already  in  the  soil,  assists  the  air  to  penetrate  more 
deeply,  thus  adding  to  its  warmth  and  promoting  weathering, 
distributes  the  bacteria,  and  discourages  the  weeds  by  prevent- 
ing their  becoming  established.  The  great  amount  of  pore  space 
which  tillage  adds  to  the  soil  may  be  realized  by  digging  a  hole 
in  any  piece  of  ground  and  then  endeavoring  to  put  back  into 
the  hole  all  the  soil  removed.  Wherever  trenches  are  dug  for 
pipes  or  tiling  we  see  an  amount  of  soil  left  over  that,  in  spite 
of  soaking  with  water  and  rammmg  with  heavy  instruments, 
cannot  be  returned  to  the  trench  from  which  it  was  dug. 

149 


150 


AGRONOMY 


Pulverizing  the  soil.  The  soil  is  pulverized  and  made  fit 
for  crops  by  plowing,  harrowing,  spading,  and  raking.  In  ex- 
tensive field  operations  the  plow  is  used  to  break  up  the  soil, 
while  the  harrow,  like  a  gigantic  rake,  is  used  to  break  up  the 
large  clods  and  level  the  surface ;  in  the  smaller  areas,  such 
as  the  home  garden,  the  same  results  are  attained  by  the  use 
of  the  spade  and  the  rake.    The  object  of  plowing  or  spading 


Fig.    107.    Plowing 

is  not  only  to  loosen  the  soil,  but  to  turn  it  over,  thus  bring- 
ing new  food  supplies  to  the  surface  and  fresh  soil  into  cul- 
tivation, while  the  topsoil,  together  with  such  fertilizers  as 
have  been  applied,  is  turned  under  to  become  fitted  for  a 
succeeding  crop.  In  humid  regions  the  soil  is  stirred  to  a  depth 
of  six  or  seven  inches,  but  in  arid  regions  the  stii-ring  may 
extend  much  deeper  without  harm  to  the  soil.  When  the  soil 
is  underlaid  by  a  stiff  and  heavy  subsoil,  the  latter  is  often 
loosened  by  subsoiling  or  trenching.  In  subsoiling  the  subsoil 
plow  follows  the  surface  plow  in  the  same  furrow  but  at  a 
greater  depth.    Trenching  is  restricted  to  small  areas  and  is 


TILLAGE  151 

done  with  a  spade.  In  this  operation  a  layer  of  soil  the  width 
and  depth  of  the  spade  is  removed,  forming  a  trench,  and  the 
soil  in  the  bottom  of  this  trench  is  loosened  by  spading.  Then 
the  trench  is  filled  by  the  soil  from  a  new  trench  adjoining  it, 
and  so  the  work  continues  until  the  last  trench  is  reached, 
when  the  first  soil  thrown  out  is  used  to  fill  it.  The  subsoil  is 
often  loosened  by  the  explosion  of  small  charges  of  dynamite. 
In  the  home  garden  the  spading  fork  is  to  be  preferred  to  the 


Photograph  by  H.  L.  Ilollister  Land  Co. 

Fig.  108.    Plowing  with  a  tractor 

On  the  larger  farms  in  the  West  a  tractor  is  often  used.   With  this  it  is  possible 
to  plow  a  dozen  or  more  furrows  at  once 

spade,  since  it  breaks  up  the  soil  more  thoroughly  and  is  more 
easily  thrust  into  stony  soil.  After  plowing  or  spading,  the 
harrow  and  rake  are  used  to  further  pulverize  the  soil.  The 
more  thoroughly  this  work  is  done,  the  better  will  be  the  seed 
bed.  Care  must  be  taken  not  to  work  the  soil  when  it  is  either 
too  wet  or  too  dry,  otherwise  the  soil  crumbs  will  be  broken 
up  and  the  soil  puddled.  A  puddled  soil  is  almost  imper- 
meable to  air,  water,  and  the  roots  of  plants.  Where  an  old 
road  or  path  across  a  field  has  been  plowed  up,  the  effects  of 


152 


AGRONOMY 


the  puddling  which  it  Ijas  undergone  is  often  apparent  for 
years  in  the  inferior  plants  along  its  course.  A  heavy  rain  in 
summer  often  puddles  the  surface  layer  of  soil  so  completely 
as  to  form  a  crust  thick  enough  to  prevent  small  seedlings 
from  forcing  their  way  up  to  the  surface. 

Mulches.  Quite  as  much  water  evaporates  from  a  saturated 
soil  as  from  a  free  water  surface.  As  fast  as  it  is  removed 
from  the  surface,  more  rises  by  capillarity  to  take  its  place. 


Photograph  by  S.  L.  Allen  &  Co.,  Philadelphia 

Fig.  109.   Cultivating  com  with  the  horse  cultivator 


The  underside  of  a  board  or  other  object  lying  on  the  ground 
is  constantly  kept  wet  by  the  rise  of  water  in  this  way.  A 
windy  day  dries  up  the  soil  by  removing  the  water  as  fast  as 
it  rises.  This  steady  loss  of  moisture  from  the  soil  can  be 
checked  by  any  sort  of  loose  cover.  The  mulch  of  stable 
manure  or  other  litter  often  spread  on  the  ground  about 
newly  planted  trees  and  shrubs  is  placed  there  for  this  pur- 
pose,  though    such  mulches  are  not  desirable  for  growing 


TILLAGE 


153 


plants  because  they  prevent  the  stirring  of  the  soil,  A  layer 
of  dry,  porous  earth  is  fully  as  effective  in  breaking  up  the 
capillary  chain.  One  of  the  main  objects  in  cultivating  plants 
is  to  maintain  a  mulch  of  this  kmd,  which  is  commonly  called 
a  dust  mulch  or  summer  mulch.  The  dust  mulch  is  also  a 
great  aid  to  the  suppression  of  weeds,  since  it  contains  so 
little   moisture  that  their  seeds  cannot  germinate.     In  dry 


I'll         I  i|  n    .  ^  1     \llui  &  Co  ,  Philadelphia 

Fig.  110.    Cultivating  witii  a  wheel  hoe 

This  imijlement  has  several  attachments  and  may  also  be  used  as  a  rake,  scarifier, 

or  hght  plow 

farming  the  dust  mulch  is  used  to  retain  the  moisture,  and  so 
effective  is  it  for  this  purpose  that  we  are  often  advised  to 
"  water  the  garden  with  a  hoe  " ;  that  is,  to  keep  the  water 
already  in  the  soil  from  escaping  by  constant  cultivation  of  the 
surface.  The  soil  should  be  loosened  after  every  rain.  When 
plants  in  large  plots  are  cultivated,  the  cultivator,  drawn  by 


154  AGRONOMY 

a  horse,  is  usually  employed ;  in  market  gardens  and  smaller 
plots  the  wheel  hoe,  operated  by  hand,  may  be  used ;  while  in 
the  home  garden  the  rake  and  hoe  are  most  frequently  seen. 
Of  the  latter  there  are  many  styles,  ranging  from  the  shuffle 
hoes  and  scarifiers  of  the  expert  gardener  to  the  common  im- 
plement found  in  every  garden.  Planting  in  long  rows  adds 
much  to  the  economy  in  any  kind  of  cultivation  and  is  abso- 
lutely necessary  when  the  wheel  hoe  or  cultivator  is  used. 

Anything  that  decreases  the  amount  of  pore  space  in  the 
soil  makes  it  easier  for  the  water  to  pass  from  one  soil  particle 
to  another,  and  thus  promotes  the  loss  of  water  through  capil- 
larity. Footprints  in  soft  soil  show  for  days,  by  their  darker 
color,  where  the  moisture  is  evaporating  most  rapidly.  In 
planting  seeds  the  escape  of  moisture  is  often  promoted  by 
compacting  the  soil  about  them,  the  cultivator  in  this  case 
being  willing  to  sacrifice  some  moisture  in  order  that  the 
growing  seeds  may  be  properly  supplied.  Covering  the  soil 
with  a  light  mulch  serves  the  same  purpose. 

Work  of  earthworms  and  ants.  Individually,  earthworms 
and  ants  are  insignificant  creatures,  seemingly  too  small  to 
have  any  effect  upon  the  soil,  but  when  their  work  in  the 
aggregate  is  considered,  they  are  seen  to  be  of  great  assistance 
in  keeping  the  soil  in  good  condition.  The  earthworms  burrow 
into  the  earth,  swallowing  bits  of  soil  and  decaying  vegetable 
matter  as  they  go,  and  later  bring  this  up  to  the  surface, 
forming  the  well-known  castings  seen  about  the  entrance  to 
their  burrows.  It  is  estimated  that  in  this  way  earthworms 
bring  up  from  lower  levels  ten  tons  of  soil  per  acre  annually, 
nearly  an  inch  in  five  years.  In  the  course  of  a  century  the 
entire  soil  as  far  down  as  cultivation  ordmarily  extends  would 
be  turned  over  and  very  thoroughly  pulverized.  In  addition, 
the  bun'ows  made  by  these  animals  aid  in  keeping  the  soil 
porous  and  well  aerated.  In  dry  soils  ants  take  the  place  of 
earthworms  and  turn  over  the  soil  nearly  as  rapidly. 


TILLAGE  155 

Rotation  of  crops.  In  some  sections  of  onr  country  there 
are  farms  upon  which  no  other  crop  than  wheat  has  ever 
been  grown ;  on  others,  cotton  or  corn  have  been  grown  con- 
tinuously. When  the  same  crop  has  been  grown  upon  one 
piece  of  land  for  a  series  of  years,  however,  there  is  a  possi- 
bility that  the  soil  may  be  depleted  of  some  necessary  element 
and  fail  to  give  adequate  returns.  Other  plants,  needing 
different  proportions  of  the  minerals,  would  be  able  to  thrive 
where  the  first  crop  would  fail.  Again,  certain  toxic  sub- 
stances excreted  by  one  set  of  plants  may  accumulate  in  the 
soil  until  they  put  an  end  to  the  healthy  growth  of  these 
plants  long  before  the  food  materials  are  exhausted,  though 
these  toxic  substances  are  not  harmful  to  other  crops.  It  has 
been  found,  also,  that  when  the  same  crop  is  grown  in  the 
same  place  for  any  length  of  time,  the  insect  and  fungous 
pests  that  trouble  it  greatly  increase  and  the  weeds  associated 
with  the  crop  multiply.  In  meadows,  daisies  often  overspread 
the  grasses,  and  wild  mustard  thrives  in  grainfields.  Ragweed 
comes  in  with  the  wheat,  and  smartweed  and  foxtail  grass  grow 
with  the  corn.  The  advantages  of  a  change  or  rotation  of 
crops  are  thus  seen  to  be  many,  and  everywhere  that  modern 
methods  obtain,  some  kind  of  rotation  is  practiced.  A  still 
further  advantage  of  crop  rotation  is  that  it  permits  the  cul- 
tivation of  deep  and  shallow-rooted  crops  alternately,  and 
thus  the  whole  soil  is  laid  under  tribute.  The  usual  rotation 
consists  of  a  grain  crop  such  as  oats  or  wheat,  a  cultivated 
crop  such  as  corn,  a  forage  crop  such  as  clover  or  alfalfa, 
and,  in  addition,  the  field  may  be  used  as  pasture  for  a  year 
or  more.  Somewhere  in  the  rotation  it  is  usually  planned  to 
have  a  legume  crop,  which,  when  finally  plowed  under,  en- 
riches the  soil  by  the  addition  of  much  nitrogen.  Even  in 
small  gardens  the  benefits  to  be  derived  from  a  rotation  of 
crops  are  worth  securing.  In  nature  there  is  also  a  more  or 
less  well-defined  rotation,    Ponds  diy  up  and  new  forms  of 


156  AGRONOMY 

vegetation  overpower  those  which  grew  in  the  water,  cUffs 
weather  to  soil  and  a  different  flora  comes  in.  In  fields  allowed 
to  lie  fallow  the  plant  covering  changes  little  by  little  for 
years,  and  in  the  waste  places  there  is  always  more  or  less 
succession  of  one  group  of  plants  by  another.  In  parts  of  our 
country  there  has  also  been  a  steady  migration  of  trees  into 
the  prairie  region  since  the  glacial  period,  and  the  movement 
is  still  gohig  on. 

PRACTICAL  EXERCISES 

1.  Visit  the  nearest  hardware  or  implement  store  and  examine  the 
machines  used  in  tilling  the  soil.  Make  a  list  of  the  kinds  seen  and 
the  uses  to  which  they  are  put. 

2.  After  a  rain  mark  off  3  sq.  yd.  in  the  open  ground.  Cover  1  sq.  yd. 
with  a  mulch  of  leaves  or  stable  manure,  pulverize  the  top  layer  of 
soil  in  the  second,  and  let  the  third  go  untouched.  At  the  end  of  a 
week  examine  as  to  moisture  content  in  the  upper  layers. 

3.  In  England  it  has  been  estimated  that  there  are  53,767  earth- 
worms to  the  acre.  Find  the  average  number  of  worms  to  the  square 
foot  in  the  school  garden  by  examining  three  different  spots,  and 
estimate  the  number  to  the  acre  upon  this  basis.  How  does  your  own 
locality  compare  with  England  in  this  respect? 

4.  Find  out  from  the  farmers  near  by  what  the  common  crop  rota- 
tions of  the  region  are.  Are  there  any  fields  in  which  rotation  is  not 
practiced?    If  so,  how  do  present  crops  compare  with  former  crops? 

5.  Make  a  table  of  the  crop  rotations  practiced  in  your  county. 

References 

Hopkins,  "  Soil  Fertility  and  Permanent  Agriculture." 
King,  "The  Soil." 

Farmers'  Bulletins 

245.  Renovating  Worn-out  Soils. 

327.  Conservation  of  Natural  Resources. 

342.  Conservation  of  Soil  Resources. 


CHAPTER  XI 

FORCING  AND  RETARDING  PLANTS 

Nature  of  the  process.  In  nature  each  species  of  plant  has 
its  own  season  of  growth  and  bloom,  determined  largely  by 
conditions  of  temperature,  moisture,  and  the  like.  Man,  by 
regulating  these  conditions,  creates  an  artificial  season,  and 
hastens,  delays,  or  extends  the  flowering  and  fruiting  period, 
thus  obtaining  his  vegetables  and  fruits  "  out  of  season  "  at 
any  time  of  the  year.  Hastening  the  development  of  a  plant 
is  called  forcing.  This  is  accomplished  by  high  temperatures, 
increased  moisture,  and  an  abundance  of  plant  food,  and  results 
in  great  succulence  and  brittleness.  Lilies,  hyacinths,  narcissi, 
and  other  bulbous  plants  are  among  those  that  are  most 
easily  brought  into  bloom  in  this  way,  either  in  our  homes  or 
in  commercial  establishments.  Owing  to  the  amount  of  food 
stored  in  their  bulbs,  they  may  even  be  forced  without  soil 
in  which  to  root,  if  they  are  kept  supplied  with  water.  On 
some  private  estates  melons,  grapes,  peaches,  strawberries, 
cucumbers,  and  tomatoes  are  produced  in  midwinter  in  houses 
devoted  to  this  purpose,  while  the  growing  of  roses,  carnations, 
clirysanthemums,  sweet  peas,  and  the  like  for  use  in  winter  is 
a  regular  business  with  the  florist.  In  the  vicinity  of  large 
cities  lettuce,  radishes,  onions,  rhubarb,  and  asparagus  are 
often  grown  in  this  way  for  the  early  markets.  The  business 
of  forcing  is  carried  on  under  glass  in  various  kinds  of  houses 
or  shelters,  but  these  all  fall  under  the  general  heads  of 
greenhouses,  cold  frames,  hotbeds,  and  hothouses. 

Retarding.  The  operation  of  holding  back  the  growth  of 
plants  for  the  production  of  blossoms  later  is  called  retarding. 

157 


158 


AGRONOMY 


This  is  the  exact  opposite  of  forcing.  All  the  early  spring  flow- 
ering plants  may  be  treated  in  this  way,  being  placed  in  cold 
storage  until  required  for  blooming.  Plants  that  have  started 
into  growth  may  be  retarded  to  a  certain  extent  by  keeping 
the  temperature  lower  than  that  required  for  vigorous  growth. 
Greenhouses  and  hothouses.  Strictly  speaking,  a  greenhouse 
is  a  building  used  for  keeping  plants  green  through  the  winter, 


Photojfraph  by  Lord  &  IJuriiham,  Kew  York 

Tig.  111.  A  glass  bouse  in  which  a  variety  of  vegetables  and  flowering  plants 
may  be  grown  during  the  winter 

and  may  or  may  not  be  heated,  depending  somewhat  on  the 
location,  while  the  hothouse  is  a  heated  building  in  which 
plants  may  be  grown,  or  warm-climate  plants  protected,  dur- 
ing the  winter.  Ordinarily,  however,  this  distinction  is  not 
maintained  and  the  terms  are  used  interchangeably.  A  con- 
servatory partakes  more  of  the  character  of  the  greenhouse, 
being  properly  a  place  for  conserving  and  showing  plants 


FORCING  AND  RETARDING  PLANTS  159 

wliich  are  grown  elsewhere.  Plant  houses  have  glass  roofs 
and  sides  to  admit  as  much  light  as  possible  during  the  short 
days  of  winter,  and  are  heated  largely  by  the  sun's  rays,  at 
least  by  day.  The  hotbed  has  been  described  as  "  a  trap  to 
catch  sunbeams,"  and  the  hothouse  is  merely  a  larger  trap. 
The  heat  rays  coming  from  the  sun  pass  through  the  glass 
easily,  but  when  reflected  back  from  the  soil  the  glass  pre- 
vents their  escape.  The  interior  therefore  warms  up  rapidly 
when  the  sun  shines.  On  bright  days  the  heat  may  be  so 
greatly  increased  as  to  injure  or  kill  the  plants  if  the  house 
is  not  ventilated.  At  night  and  on  very  cold  days  the  warmth 
is  maintained  by  some  sort  of  artificial  heating  system.  The 
first  hothouses  were  kept  warm  by  quantities  of  fermenting 
manure  placed  in  pits  beneath  the  benches  upon  which  the 
plants  were  grown,  and  such  means  may  still  be  depended 
upon  to  keep  the  frost  out  of  small  houses  during  the  winter. 
In  general,  however,  some  sort  of  hot-water  heating  system 
is  used. 

Hotbeds.  Hotbeds  are  really  small  plant  houses  kept  warm 
by  fermenting  manure  and  the  sun's  heat,  and  are  used  for 
growing  plants  before  the  weather  will  permit  of  their  being 
grown  in  the  open.  Early  crops  of  lettuce,  radishes,  and  other 
vegetables  are  raised  in  this  way,  and  long-season  crops,  such 
as  tomatoes,  peppers,  and  eggplants,  are  started  here  and 
carried  along  until  transplanting  time.  To  make  a  hotbed,  a 
pit  should  be  dug  2  feet  deep  and  about  1  foot  wider  than 
the  frame  that  is  to  be  placed  over  it.  This  pit  is  to  be  filled 
with  manure  to  supply  the  heat,  and  should  contain  a  good 
share  of  straw  or  other  material  in  order  that  the  heat  may 
be  long  continued.  The  manure  should  be  placed  in  a  pile 
and  forked  over  at  intervals  for  several  days  before  using,  to 
insure  that  the  fermenting  material  has  been  thoroughly  mixed 
through  it.  When  the  whole  pile  is  steaming  it  should  be 
placed  in  the  pit  in  layers  about  6  inches  deep,  and  each  layer 


160 


AGRONOMY 


thoroughly  tramped  down.  Over  the  pit  of  manure  a  layer  of 
good  soil  6  inches  deep  should  be  spread,  and  m  this  the 
plants  are  grown.  The  hotbed  frame  is  made  of  boards,  and 
the  roof,  which  is  made  of  one  or  more  hotbed  sashes,  should 
slope  toward  the  south.  The  front  of  the  bed  may  be  6  inches 
or  1  foot  high  and  the  back  12  to  20  inches.  Hotbed  sashes 
are  3  by  6  feet  in  size,  and  the  frame  is  made  about  6  feet 
wide  and  long  enough  to  take  one  or  more  sashes.  Old  win- 
dow sash  may  be  used  if  hotbed  sash  are  not  at  hand.  When 
the  manure  is  first  put  into  the  pit  and  the  sashes  put  on, 
the  heat  often  rises  too  high  for  plant  growth.  Seeds  should 
not  be  planted  until  the  temperature  at  midday  falls  below 

90°.  The  frame  is  usually 
banked  up  on  the  outside 
with  manure  as  an  addi- 
tional protection  from  the 
cold,  and  on  very  cold 
nights  the  glass  should  be 
covered  by  mats,  old  car- 
pets, or  a  layer  of  straw. 
Hotbeds  are  sometimes 
made  upon  a  level  pile  of  manure  placed  on  the  surface  of 
the  ground.  In  this  case  the  manure  should  project  beyond 
the  frame  at  least  a  foot  on  all  sides.  The  heat  in  a  hotbed 
is  not  sufficient  to  carry  it  tlirough  the  entire  winter,  and  its 
use  is  usually  confined  to  the  late  winter  and  spring.  In  the 
Northern  states  the  hotbed  is  not  begun  much  before  the 
middle  of  February,  and  in  many  cases  the  middle  or  end  of 
March  is  early  enough.  In  managing  the  hotbed  care  should 
be  taken  to  give  the  plants  air  whenever  the  weather  is  favor- 
able. This  may  be  accomplished  by  lifting  the  lower  end  of 
the  sash  and  placing  a  block  under  it,  or  on  fine  days  the  sash 
may  be  shoved  part  way  off  the  frame.  Plenty  of  air  tends  to 
make  the  plants  sturdier. 


Fig.  112. 


A  hotbed  showing 
of  construction 


the  details 


FORCING  AND  RETARDING  PLANTS  161 

Cold  frames.  The  cold  frame  differs  from  the  hotbed  in  a 
single  feature:  it  lacks  the  pit  of  manure.  It  cannot  therefore 
be  used  for  growing  plants  in  very  cold  weather,  though  as 
the  air  becomes  warmer  in  spring  it  is  often  used  to  start 
tomato,  cabbage,  and  other  plants  for  transplanting.  Its  great- 
est usefulness  is  found  in  carrying  half-hardy  plants  over  the 
winter  and  in  prolonging  the  growing  season  of  lettuce, 
radishes,  pansies,  and  the  like  in  autumn.  Cold  frames  are 
banked  up  with  manure  to  aid  in  keeping  out  the  frost,  and 
in  severe  weather  may  be  covered  with  mats.  Both  cold  frames 
and  hotbeds  do  best  if  placed  in  sheltered  situations,  though 
cold  frames  for  carrying  half-hardy  or  dormant  plants  through 
the  winter  are  often  placed  on  the  north  side  of  a  fence  or 
building.  In  the  latter  case  the  object  is  simply  to  protect 
the  plants,  and  no  light  is  needed.  Cold  frames  designed  to 
shelter  plants  for  a  few  weeks  in  spring  may  be  made  with 
oiled  paper  or  cloth  in  place  of  the  glazed  sash. 

Forcing  single  hills.  Single  plants  of  such  species  as  rhu- 
barb, asparagus,  and  sea  kale  may  be  made  to  grow  much 
earlier  than  they  would  naturally,  by  placing  a  box  or  liaH 
barrel  over  each  hill  and  piling  manure  around  it.  The  top  is 
sometimes  covered  with  a  light  of  glass,  thus  making  a  mini- 
ature cold  frame  of  it.  Single  boxes  of  this  kind  are  now  being 
offered  for  sale  and  serve  a  variety  of  purposes.  In  autumn 
manure  is  often  piled  over  hills  intended  for  forcing,  to  keep 
the  ground  from  freezing  deeply.  Asparagus,  rhubarb,  and 
onions  are  often  forced  in  the  house  by  setting  the  ''roots" 
upright  and  close  together  in  a  box  and  placing  the  box  in  a 
warm  room  or  cellar.  If  kept  moist,  the  young  shoots  will 
soon  appear.  These  plants  may  also  be  grown  under  the 
greenhouse  benches  in  the  same  way.  Light  is  not  necessary 
for  forcing  plants  of  this  nature,  since  the  food  stored  in  the 
roots  or  other  underground  parts  is  drawn  upon  for  making 
shoots.    If  it  is  desii'ed  to  force  the  same  roots  again,  they 


162  AGRONOMY 

must  be  set  out  in  spring  in  good  soil  and  allowed  one  or 
more  years  in  which  to  recuperate. 

Etherization.  A  large  number  of  plants  that  form  their 
flower  buds  at  the  end  of  the  growing  season  do  not  readily 
resume  growth  when  kept  in  sufficient  warmth.  These  same 
plants,  however,  if  allowed  to  remain  dormant  and  brought 
into  warmth  at  the  end  of  winter,  begin  at  once  to  grow.  From 
this  it  is  seen  that  plants  require  a  season  of  rest,  and  if  we 
are  to  induce  such  species  to  bloom  in  midwinter,  something 
to  take  the  place  of  this  rest  must  be  devised.  Freezing,  as  a 
substitute  for  rest,  has  been  found  useful.  If  rhubarb  plants 
designed  for  indoor  forcing  are  carried  in  before  frost,  they 
fail  to  make  proper  growth,  but  if  dug  up  in  the  field  and 
exposed  to  a  few  frosts,  they  grow  at  once  when  planted. 
Heat  appears  to  have  the  same  effect  as  cold,  and  many  spe- 
cies may  be  as  easily  forced  by  plunging  their  branches  into 
hot  water  for  a  short  time.  Drought  also  affects  plants  like 
cold,  and  some  specimens  behave  in  the  same  way  if  treated 
with  ether.  In  etherization  the  plants  are  placed  in  an  air-tight 
receptacle  and  exposed  to  the  fumes  of  ether  for  twenty-four 
hours  or  longer.  When  brought  into  warmth  they  are  ready 
to  grow,  the  ether  appearing  to  have  the  same  effect  upon 
them  as  the  long  rest  through  the  winter.  Lilacs  etherized  in 
August  have  been  brought  into  full  bloom  a  few  weeks  later. 
In  etherization  about  one  third  of  an  ounce  of  ether  to  each 
cubic  foot  of  space  is  the  right  amount. 

Forcing  plants  in  the  window  garden.  The  conditions  in 
most  dwellings  are  not  favorable  to  plant  growth,  especially  in 
winter.  The  dryness  of  the  air,  the  lack  of  sunlight,  the  pres- 
ence of  coal  gas  and  illuminating  gas  in  the  air,  and  the  differ- 
ence between  the  day  and  night  temperatures  all  conspire  to 
kill  or  enfeeble  vegetation.  Only  the  hardiest  plants  can  be 
induced  to  grow  and  bloom  under  such  circumstances.  Plants 
produced  from  bulbs,  corms,  and  the  like  are  an  exception  to 


FORCIKG  AND  RETARDING  PLANTS  163 

this,  since  the  food  necessary  for  their  growth  and  even  the 
blossoms  themselves  are  formed  in  the  underground  parts  dur- 
ing the  preceding  season.  If  given  sufficient  water  they  are 
able  to  develop  their  flowers  with  very  little  light,  since  blos- 
soming with  them  is  largely  a  mere  expansion  of  parts  already 
formed.  They  may  be  grown  in  soil  or  water,  but  in  either 
case  they  are  usually  set  aside  in  some  cool  dark  place,  after 
planting,  to  form  roots  before  being  placed  in  the  light.  The 
most  popular  subjects  for  growmg  in  this  way  are  the  paper- 
white  narcissus  and  the  Chinese  sacred  lily,  a  closely  related 
species,  but  tulips,  crocuses,  hyacinths,  and  other  bulbous  plants 
are  also  grown.  After  flowering,  the  plants  are  usually  thrown 
away,  since  they  cannot  be  satisfactorily  forced  a  second  time. 

PRACTICAL  EXERCISES 

1.  At  the  proper  time  make  a  hotbed  or  cold  frame  in  the  school 
garden  and  plant  in  it  seeds  of  long-season  plants  that  may  be  trans- 
planted to  the  open  ground  later.  Make  a  sowing  of  lettuce,  beets,  or 
onions  for  transplanting. 

2.  Dig  up  spring  flowering  plants  before  they  start  into  growth  and 
place  in  cold  storage,  to  be  brought  out  and  flowered  when  those  in  the 
fields  have  gone. 

3.  Try  forcing  sea  kale,  asparagus,  or  rhubarb. 

4.  Make  a  single  forcing  hill  for  growing  some  jilant  from  seeds, 
such  as  melon. 

5.  Try  forcing  some  wild  plant  at  the  beginning  of  winter.  Etherize 
another  plant  of  the  same  kind  and  com[)are  results. 

References 

Bailey,  "The  Forcing  Book." 
Bailey,  "Manual  of  Gardening." 


CHAPTER  XII 

WEEDS 


Definition  of  a  weed.  A  weed  is  properly  defined  as  a  plant 
out  of  place.  No  matter  how  beautiful  the  flowers  may  be,  or 
how  highly  the  species  may  be  regarded  for  decorative  planting, 
if  it  competes  with  cultivated  plants  for  possession  of  the  soil, 


Photo^'raph  from AiTierican  Stetl  anil  Wire  Co. 


Fig.  113.    Spraying  a  field  of  young  grain  witli  iron  sulpliate  to 
eradicate  mustard  and  otlier  weeds 

it  is  a  weed.  In  some  localities  the  worst  Aveeds  with  which 
the  farmer  has  to  contend  are  ferns.  Many  species  that  in 
foreign  lands  are  cherished  as  beautiful  flowering  plants  are 
counted  mere  weeds  at  home.  Indeed,  some  of  the  weeds  that 
now  bother  our  cultivated  crops,  such  as  bouncing  Bet  and 

164 


WEEDS  165 

toadflax,  were  originally  brought  from  Europe  as  desirable 
additions  to  the  flower  garden,  and  only  later  took  up  a  free 
life  in  the  fields.  A  few  of  our  weeds  are  native,  but  most  of 
our  noxious  species  have  been  derived  from  the  Old  World, 
where  centuries  of  struggle  with  crop  and  cultivator  have 
developed  to  the  utmost  their  ability  to  resist  all  attempts  to 
dislodge  them.  Nor  are  weeds  entirely  confined  to  specimens 
growing  in  cultivated  areas.    The  plants  that  come  up  in  walks 


Photograph  from  American  Steel  and  Wire  Co. 

Fig.  114.    Graiiifiekl  showing  the  effect  of  spraying  with  iron  sulphate 
The  portion  on  the  left  is  unsprayed.    Note  the  abundant  young  mustard  plants 

and  drives,  on  railway  embankments,  and  in  similar  places  are 
weeds.  Other  weeds,  like  the  ditch  moss  and  water  hyacinth, 
are  confined  to  the  water,  but  prove  their  weediness  by  chok- 
ing up  the  streams  and  rivers,  and  in  some  cases  actually 
preventing  navigation. 

Harmfulness  of  weeds.  Weeds  are  harmful  in  several  ways. 
They  absorb  water  needed  for  the  growth  of  cultivated  crops, 
prevent  the  formation  of  plant  food  by  shading,  harbor  fungous 
and  insect  enemies,  render  more  difficult  the  task  of  keeping 


166 


AGRONOMY 


the  soil  loose  and  open,  and  in  many:  cases  their  seeds  gathered 
with  the  crop  injure  its  value.  Weeds  should  not  be  allowed 
to  grow  even  in  the  borders  of  cultivated  grounds,  since  from 
this  point  they  may  seed  the  soil  for  several  years  to  come. 
In  this  connection  it  is  well  to  remember  the  oft-tiuoted 
maxim,  "  One  year's  seeds,  seven  years'  weeds." 


Photograph  from  American  Steel  and  Wire  Co. 

Fig.  115.    A  grainfleld  showing  wild  mustard  in  blossom.    The  portion  on 
the  right  has  been  sprayed  with  iron  sulphate 


Nature  of  weeds.  Some  of  the  qualities  that  conduce  to 
weediness  in  plants  are  abundant  and  easily  distributed  seeds, 
the  ability  to  grow  rapidly,  to  endure  injury  and  shading,  and 
to  tlirive  upon  little  moisture  and  in  sterile  soils.  Many  secure 
immunity  from  grazing  animals  by  offensive  odors,  prickly 
leaves  and  stems,  and  other  disagreeable  characteristics.  Some 
are  winter  annuals  that  grow  in  spring  before  more  valuable 
crops  have  started ;  others  are  summer  annuals  that  wait  until 


WEEDS 


167 


the  crops  are  well  along,  but  grow  so  rapidly  when  they  do 
appear  that  they  soon  overtake  and  choke  out  their  competi- 
tors; while  still  others  are  perennials  that  spring  again  and 
again  from  underground  parts  after  being  cut  down  by  the 
gardener.  A  few  are  mat  plants  or  rosette  plants  that  form 
dense  carpets  over  the  soil,  and  some  are  vines  that  climb  on 
other  plants,  but  the  great  majority  simply  grow  erect  and  take 
the  ground  by  virtue  of  a  more  luxuriant  growth. 


Plioto^'rapli  from  American  Steel  and  Wire  Co. 

Fig.  116.    Spraying  a  lawn  with  a  baud  sprayer  to  eradicate  weeds 


Eradicating  weeds.  One  of  the  most  effectual  methods  of 
eradicating  weeds  is  to  prevent  them  from  seeding.  All  annual 
species  are  easily  held  in  check  in  this  way.  When  crops  are 
frequently  cultivated  the  weeds  are  unable  to  get  a  start.  A 
favorite  way  of  clearing  a  field  of  weeds  is  to  plant  it  for  one 
or  more  seasons  to  some  crop  that  must  be  hand  cultivated. 
All  weeds  may  be  killed  by  applications  of  salt,  but  since  what 
will  kill  weeds  will  also  kill  more  valuable  plants,  this  method 
cannot  be  used  except  on  walks,  drives,  and  similar  places. 
Asparagus,  however,  can  stand  an  application  of  salt  strong 
enough  to  kill  the  weeds  that  grow  with  it.    Plants  which 


168 


AGRONOMY 


depend  upon  peculiar  soil  conditions  may  be  eradicated  by 
changing  these  conditions.  Sedges  which  delight  in  moist  soil 
may  be  exterminated  by  draining,  and  mosses,  sorrel,  and  various 
other  plants  that  like  acid  soils  may  be  driven  out  by  Imiing 
the  soil.  Perennial  plants  must  either  be  starved  out  by  fre- 
quently cutting  off  the  leaves,  or  they  may  be  dug  up.  A 
large  number  of  weeds  are  also  killed  by  spraying  with  iron 
sulphate,  or  "  copperas,"  in  the  proportion  of  six  pounds  of  iron 


Fiioto^rapk  from  Bergen  and  Caldwell's  '•  Practical  Botany  " 

Fig.  117.   A  tumbleweed  {Cycloloma)  blown  into  heaps  by  the  wind 

sulphate  to  four  gallons  of  water.  Grainfields  may  be  practi- 
cally freed  from  wild  mustard  in  this  way,  the  spray  doing  no 
harm  to  the  cultivated  plants.  All  crops  are  not  so  resistant 
and  one  must  discover  what  the  particular  requirements  of  a 
crop  are  before  spraying.  For  destroying  algse,  the  fine,  fila- 
mentous green  growths  that  often  appear  in  lily  ponds  and  the 
like,  copper  sulphate  is  often  used.  The  water  should  be  treated 
with  one  part  copper  sulphate  to  three  million  parts  of  water. 
Fish  are  very  easily  poisoned  by  this  substance,  and  care  must 


WEEDS 


169 


be  taken  not  to  have  it  too  strong  if  used  in  ponds  in  which 
there  are  desirable  species. 

Not  all  weeds  are  equally  noxious  ;  moreover,  what  may  be 
a  bad  weed  in  one  locality  may  be  comparatively  harmless  in 
another,  perhaps  because  the  crops  are  different,  but  there  are 
some  species  whose  reputation  for  noxious  qualities  is  world- 
wide. Some  of  these  are  listed  here.  Other  and  more  local 
species  may  be  studied  in  books  devoted  to  the  subject. 


l'liotoj;rai)h  from  American  Steel  and  Wire  Co. 

Fig.  118.    Dandelions  gone  to  seed  on  a  neglected  lawn 

Purslane  (^Portulaca  oleracea).  This  is  a  fleshy  little  mat 
plant  with  small  yellowish  flowers  that  open  only  in  sunshine, 
and  is  related  to  the  portulaca,  or  rose  moss,  of  our  flower 
gardens.  It  will  grow  in  almost  any  soil,  and  stores  so  much 
water  in  its  thick  leaves  that,  after  it  has  begun  to  bloom,  it 
can  ripen  its  seeds  though  severed  from  the  soil. 

Spreading  amaranth  (^Amaranthua  hlitoides).  This  species 
resembles  the  purslane,  but  it  is  larger,  less  fleshy,  and  has 
clusters  of  insignificant  greenish  flowers.  Single  specimens 
may  form  mats  more  than  a  yard  across. 


170 


AGRONOMY 


Green  amaranth  QAmaranthus  hyhridus).  This  is  also  known 
as  redroot  and  pigweed.  It  grows  to  the  height  of  several  feet, 
with  broad  coarse  leaves  topped  by  a  dense  pyramid  of  green- 
ish flowers.    It  is  a  most  abundant  and  well-known  weed,  but 

is  easily  extermmated. 

Tumbleweed  (^Amaran- 
thus  albus).  Before  the 
advent  of  the  so-called 
Russian  thistle  this  was 
the  best-known  tumble- 
weed.  It  is  a  rather  low 
plant  with  branches  dis- 
posed in  globular  form. 
When  mature,  the  whole 
plant  separates  from  the 
root  and  is  blown  about 
the  country,  scattering 
the  minute  seeds  as  it 
goes. 

Pigweed  (  Chenopodium 
album).  This  weed  is 
also  known  as  lamb's 
quarters.  It  is  a  pale 
green  plant  with  some- 
what triangular  leaves 
that  are  wliitened  by  a 
mealy  deposit,  and  is  thus  easily  recognized.  It  is  a  close  ally 
of  the  beet  and  spinach  and  is  often  eaten  as  a  pot  herb. 

Russian  thistle  (^Salsola  tragus').  This  plant  is  ui  no  sense 
a  thistle,  being  more  closely  related  to  the  pigweeds.  It  is 
extremely  prickly,  and  from  this  circumstance  its  name  is 
derived.  It  is  another  of  the  tumbleweeds  and  in  conse- 
quence spreads  rapidly.  It  is  well  known  in  the  Middle  West, 
where  it  was  accidentally  introduced  during  the  latter  part  of 


Photograph  from  American  Steel  and  Wire  Co. 

Fig.  119.   The  common  plantain 


WEEDS 


171 


the  last  century,  and  is  now  a  familiar  plant  in  waste  grounds, 
roadsides,  railway  embankments,  and  the  like. 

Spotted  spurge  (^Euphorbia  maculata).  The  spotted  spurge 
is  anotlier  of  the  mat  plants,  and  is  readily  distinguished  by  its 
small,  thin,  hairy  leaves  with  a  red  blotch  in  the  center,  and 
by  its  much-branched  slender  stem,  pressed  close  to  the  earth. 
The  juice  is  milky.  It  delights  in  dry  open  places  and  grows 
readily  in  soils  too  sterile  for  the  growth  of  other  plants. 


Photograph  t'l 

Fig.  120.  A  tangle  of  the  common  bindweed 


?teel  aud  Wire  Co. 


Dandelion  (^Taraxacum  officinale).  Its  yellow  flowers  and 
feathery  heads  of  seeds  make  this  most  abundant  rosette  plant 
too  well  known  to  require  description.  Its  long  and  fleshy 
taproot  is  often  removed  by  digging,  but  if  any  is  left  in  the 
soil,  it  may  origmate  new  buds  and  produce  a  dozen  or  more 
plants  where  but  one  was  originally. 

Plantain  (Plantago  sp.).  Tliree  species  of  plantain  are 
frequent  as  weeds  in  grassy  areas.    Of  these,  Plantago  major 


172 


AGRONOMY 


and  P.  Rugelii  are  common  dooryard  weeds  with  broad  and 
rounded  leaves  and  slender  spikes  of  inconspicuous  flowers. 
The  third  species,  the  narrow-leaved  plantain  (P.  lanccolata)^ 
is  easily  distinguished  by  its  rosette  of  long  narrow  leaves 

veined  lengthwise  of  the 
blade.  All  the  plantains 
are  easily  dug  up. 

Common  bindweed  (Con- 
volvulus sepiuni).  The 
large  white  or  pink  fun- 
nel-shaped flowers,  like 
morning-glories,  make  the 
bindweed  conspicuous 
and  well  known.  It  is 
fond  of  rich  soil  and 
forms  tangled  mats  over 
the  vegetation  in  the 
fields  where  it  grows.  It 
has  a  creeping  under- 
ground rootstock  that 
makes  it  one  of  the  hard- 
est of  weeds  to  eradicate. 
Black  bindweed  (^Poly- 
gonum convolvulus^.  The 
climbing  stems  of  this 
plant  overrun  other  plants 
in  its  vicinity,  after  the 
manner  of  the  common 
bindweed,  to  which,  how- 
ever, it  is  not  closely  related.  It  is  a  much  slenderer  plant 
with  greenish  flowers  and  seeds  that  suggest  its  relative  the 
buckwheat.  Being  annual  instead  of  perennial,  it  is  a  much 
less  formidable  species  than  the  common  bindweed,  though 
its  vigorous  growth  makes  it  a  harmful  weed. 


Photograph  from  American  Steel  and  Wire  Co. 

Fig.  121.    A  common  wild  lettuce  related 
to  the  prickly  lettuce 


WEEDS 


173 


Prickly  lettuce  (Lactuca  scariola).  Although  the  intro- 
duction of  this  plant  into  America  occurred  but  recently,  it 
has  already  spread  so  extensively  as  to  become  a  common 
weed.  It  may  be  known  by  its  erect  prickly  stems  and  bluish- 
green  leaves,  most  of  which  are  turned  edgewise  and  point 
north  and  south.  It  is  frequently  a  winter  annual  and  is  re- 
garded by  botanists  as  being  the  parent  of  our  garden  lettuce. 

Ragweed  (^Ambrosia 
artemisicefoUd).  Rag- 
weed, a  homely  plant 
with  much-dissected 
leaves,  is  found  al- 
most everywhere  in 
cultivated  land.  At 
flowering  time  the  in- 
significant greenish- 
yellow  flowers  shed 
great  quantities  of  yel- 
low, dustlike  pollen, 
which  collects  upon  the 
shoes  and  clothing  of 
all  who  pass  through  it. 
The  pollen  is  regarded 
with  good  reason  as  be- 
ing one  of  the  causes 
of  hay  fever. 

Wild  mustard  (Bras- 
sica  arvends).  Several  species  of  mustard  are  known  under 
the  general  name  of  wild  mustard,  but  the  species  named  above 
is  the  most  widespread  and  troublesome.  The  mustards  may 
be  distinguished  by  their  coarse  hairy  leaves,  clusters  of  bright 
yellow  flowers,  and  long  spikes  of  seed  pods.  They  spring  up 
quickly,  grow  rapidly,  and  soon  smother  less  strenuous  plants. 
The  turnip  is  a  closely  related  species  of  Brassica. 


Photograph  troin  American  Steel  and  Wire  Co. 

Fig.  122.   Ragweed,  a  common  weed  regarded 
as  the  cause  of  hay  fever 


174 


AGRONOMY 


Oxeye  daisy  (^Chrysanthemum  leucanthemtwi).  The  large 
white  flowers  of  this  species,  universally  known  as  daisies  or 
marguerites,  are  sufficient  to  identify  it.  It  is  a  perennial, 
spreading  rapidly  by  means  of  its  many  small  seeds,  and  be- 
comes a  bad  weed  in  meadows  and  pastures,  crowding  out  the 

rightful  tenants  of 
the  soil.  It  is  some- 
times known  as 
whiteweed.  The 
yellow  daisy  (Rud- 
heckia  hirta),  also 
common  in  fields 
and  meadows,  is  a 
native  species. 

Canada  thistle 
(Cnious  arvensiii). 
Many  other  spe- 
cies of  thistle  are 
confused  with  this 
much-dreaded  plant, 
which,  in  spite  of 
the  name  it  bears, 
is  an  Old  World 
species,  and  not  a 
native  of  this  con- 
tinent. It  may  be 
known  by  its  very 


Photograph  from  American  Steel  and  Wire  Co. 

Fig.  123.   A  plant  of  wild  mustard 
This  species  is  especially  harmful  in  grainfields 


prickly  stems  and  leaves  and  its  pale  lavender  blossoms  of 
small  size.  Owing  to  the  fact  that  its  rootstock  is  widely 
creeping  and  deep  in  the  earth,  it  is  very  difficult  to  eradicate 
when  once  established.  The  plant  has  two  kmds  of  blossoms, 
those  on  some  specimens  being  completely  sterile.  This  has 
given  the  impression  in  some  sections  that  the  plant  does  not 
ripen  good  seeds  in  parts  of  its  range. 


WEEDS  175 

Quack  grass  (^Agropyrum  repens).  This  is  a  perennial  species 
whose  slender  and  wide-creeping  rootstock  sends  up  new  stems 
at  frequent  intervals  that  later  bear  slender  close-set  spikes  of 
greenish  flowers.  It  is  one  of  the  hardest  of  weeds  to  root  out, 
but  this  may  be  accomplished  by  planting  fields  infested  with 
it  to  some  hoed  crop  and  cultivating  frequently.  Though  so 
generally  useless,  this  species  is  closely  related  to  the  wheat. 


Photograph  from  American  Steel  aud  Wire  Co. 

Fig.  124.   The  oxeye  daisy  on  the  border  of  a  field 

Crab  grass  (^Panicum  sanguinale).  This  species,  often  called 
finger  grass,  is  a  coarse  annual  that  does  not  begin  to  grow 
until  the  weather  is  quite  warm  and  the  cultivated  crops  well 
started.  At  first  the  stems  are  erect,  but  later  they  lie  upon 
the  soil  with  only  the  tips  erect,  and  root  wherever  a  joint 
comes  in  contact  with  the  earth.  When  pulling  it  up,  every 
root  must  be  loosened  or  it  will  continue  to  thrive.  The  flow- 
ering stems  are  topped  by  several  slender  spikes  that  radiate 
from  a  common  center. 


176 


AGKONOMY 


Foxtail  (^Setaria  glauca).  This  is  another  annual  grass  that 
does  not  make  its  appearance  until  very  late  in  spring.  It  has 
a  most  extensive  root  system,  and  when  it  is  pulled  up  often 
brings  more  valuable  plants  with  it.  The  fruiting  part  is  a 
bristly  spike  two  or  three  inches  long,  from  the  appearance 

of  which  the  common 
name  is  derived. 

Old  witch  grass  (I^an- 
icum  capillare).  This  is 
an  annual  that  thrives 
in  dry  soils.  It  appears 
in  early  summer,  put- 
ting up  several  coarse 
hairy  stems  that  bear 
large  panicles  of  many 
purplish  threadlike  di- 
visions. Late  in  the  year 
these  panicles  break 
from  the  plant  and  are 
blown  about  by  the 
wind.  This  species  is 
sometimes  called  tickle 
grass  in  allusion  to  its 
feathery  panicle. 

Photograph  from  Ainericaii  Steel  and  Wire  Co.  ButtCrCUD      (  HdnUTl- 

FiG.  125.    Youns  plant  of  the  Canada  thistle,  -,  •  \       o  i 

°^  ^        -  '     cuius   acris).    several 

one  of  our  worst  weeds  ^ 

species  of  buttercup 
may  become  weeds,  but  the  one  here  given  is  best  entitled  to 
the  name.  It  takes  entire  possession  of  many  damp  meadows 
and  is  so  acrid  that  cattle  will  not  touch  it.  Drying  dispels 
the  acrid  properties,  and  when  cut  with  the  hay  it  is  harmless. 
Wild  carrot  (Daucus  carota).  The  wild  carrot  is  also  called 
bird's  nest  and  Queen  Anne's  lace,  in  allusion  to  its  flower 
clusters.    It  is  a  vile  pest  in  many  thin  soils  and  its  sturdy 


WEEDS 


177 


taproot  makes  it  hard  to  conquer.  The  plant  is  supposed 
to  be  identical  with  the  cultivated  carrot,  but  in  the  wild 
state  it  is  reputed  to 
be  poisonous. 

Sorrel  (Rumex  aceto- 
sella).  This  plant,  com- 
monly known  as  sour 
grass  or  horse  sorrel, 
is  a  perennial  weed 
with  numerous  creep- 
ing subterranean  stems 
and  thrives  in  sterile 
soil.  Early  in  summer 
it  turns  its  haunts  a 
rusty  red  by  a  multi- 
tude of  small  flowers.  It  is  supposed  to  be  an  indicator  of 
acid  soils  and  may  be  controlled  by  the  application  of  lime. 


t 

S 

1;^-:^ 

,;-'  V"'-  >-'^-i' 

■-'  -   V:.-..^i 

Fig.  126.    Wild  carrot  on  a  neglected  lawn 


Photograph  from  American  Steel  and  Wire  Co. 

Fig.  127.   A  field  overrun  by  wild  carrot 

Other  weeds.  Among  less  noxious  though  ever-present  weeds 
may  be  mentioned  shepherd' s-purse  (Capsella),  pepper-grass 


178  AGRONOMY 

(JLepidium),  chickweed  (^Stellaria),  knotgrass  (^Polygonum), 
burdock  (^Arctiwn),  evening  primrose  (Oenothera),  sneezeweed 
(Helenium'),  bugloss  (Eehium),  bouncing  Bet  (Saponaria'), 
toadflax  (Linaria),  smartweed  (Polygonum),  dog  fennel  (^An- 
tJiemis),  and  Jimson  weed  (^Datura).  These  may  be  looked  up 
in  any  botanical  manual.  A  large  number  of  other  plants, 
such  as  yarrow  (^Achillea)  and  sheep  sorrel  (^Oxalis),  come 


> 

•       "  -^  ,  *•    • 

• 

* 

i 

'  ""^-:% 

^^A 

\^ 

^T^^*' 

WW^, 

Ml          i'.* 

Photograph  from  Aniencuu  Stetl  and  Wire  Co. 

Fig    128.    A  plant  of  dog  fennel,  a  common  weed  along  roadsides  and  in 

low  grounds 

under  the  designation  of  weeds,  since  they  frequently  grow 
among  cultivated  crops,  but  they  are  seldom  harmful  enough 
to  be  classed  with  the  noxious  species  and  are  not  difficult 
to  eradicate. 

It  should  not  be  supposed  that  the  plants  we  now  recognize 
as  weeds  are  the  only  ones  with  which  the  cultivator  is  likely 
to  have  to  contend.  New  weeds  are  practically  certain  to  ap- 
pear from  time  to  time,  either  derived  from  our  native  flora 


WEEDS 


179 


or  as  immigrants  from  other  parts  of  the  world.  The  orange 
hawkweed  {Hieracium  aurantiacum),  which  within  a  generation 
has  spread  over  large  areas  in  the  Eastern  states,  is  a  case  in 
point,  and  the  Russian  thistle,  which  appeared  somewhat 
earlier,  is  another.  The  rapidity  with  which  these  weeds  have 
spread  is  accounted  for  by  their  methods  of  seed  distribution. 
Plants  with  wind-dis- 
tributed seeds  are 
usually  good  travel- 
ers, but  those  whose 
seeds  lack  special 
means  of  distribution 
are  often  very  slow 
in  conquering  new 
territory.  The  ox  eye 
daisy,  which  has 
proved  such  a  pest 
in  New  England,  is 
still  rare  or  absent 
in  the  north -central 
states,  while  the  yel- 
low daisy,  originally 
a  Western  plant,  has 
spread  to  the  East  in 
comparatively  recent 
times.     New    weeds 

are  likely  to  be  first  found  along  traveled  ways,  especially  if 
their  seeds  are  not  modified  in  some  way  for  distribution,  and 
a  new  line  of  traffic  is  usually  responsible  for  their  introduc- 
tion. Galinsoga  parvijlora,  a  harmless  Mexican  plant,  was 
unknown  in  the  Northern  and  Eastern  states  until  the  inhabit- 
ants began  railway  traffic  with  Mexico.  Now  it  is  common  in 
many  places  as  far  north  as  Canada.  The  teasel  is  an  Old 
World  plant  that  has  long  been  known  as  a  weed  in  America, 


- 

fr 

^^ti 

IP»|/^ 

-  ••'^  1 

r  Jm'^ 

fg 

-.■iJWCT 

^8 

r 

Fig.  129. 


Photograph  from  AmericaD  Steel  and  Wire  Co. 

Yarrow,  a  nearly  harmless  weed  of 
wide  distribution 


180  AGRONOMY 

but  it  is  still  rare  except  in  the  vicinity  of  railroads.  Other 
weeds  owe  their  appearance  in  new  regions  to  their  having 
been  brought  in  with  the  seeds  of  cultivated  crops.  The  corn 
cockle  (^A(/ro8temma  githago^  owes  its  common  name  to  the 
fact  that  it  is  nearly  always  found  in  grainfields,  where  its 
seeds  have  l^een  carried  with  the  grain. 

PRACTICAL  EXERCISES 

1.  Make  a  list  of  the  weeds  known  to  grow  in  your  locality. 

2.  AVliat  qualities  make  them  bad  weeds  ? 

3.  Make  a  list  of  the  weeds  that  spring  up  in  the  school  garden. 

4.  Underscore  the  weeds  in  the  above  lists  that  are  perennials. 

5.  Make  a  collection  of  weed  seeds  labeled  with  both  scientific  and 
common  names. 

6.  Make  a  list  of  the  ways  in  which  these  weed  seeds  are  distributed, 
with  examples  of  each. 

7.  Estimate  the  number  of  seeds  produced  by  one  weed  in  a  season. 
If  all  these  seeds  should  grow  the  following  year  and  produce  the  same 
number  of  seeds  and  continue  to  reproduce  in  this  way,  how  many  years 
would  it  take  to  produce  one  plant  for  each  acre  of  land  in  the  world  ? 

8.  Make  a  list  of  weeds  that  have  come  into  your  region  with  the 
seeds  of  cultivated  crops.  Make  a  similar  list  for  those  that  have  come 
in  along  the  railroads. 

References 

Long,  "Common  Weeds  of  the  Farm  and  Garden." 
Pammel,  "  Weeds  of  the  Farm  and  Garden." 

Farmers'  Bulletins 

28.  AVeeds  and  how  to  kill  them. 
188.  Weeds  used  as  Medicines. 

Bureau  of  Plant  Industry 

8.3.  The  Vitality  of  Buried  Seeds. 
89.  Wild  Medicinal  Plants  of  the  United  States. 
107.  American  Root  Drugs. 


CHAPTER   XIII 


PROPAGATION 


Natural  methods.  The  one  means  by  which  all  plants  higher 
in  the  scale  of  life  than  the  ferns  are  multiplied  is  by  seeds. 
Many  species,  in  addition  to- 
this,  have  devised  various 
ways  of  multiplying  asez- 
ually  or  vegetatively  by 
means  of  special  parts  of 
the  plant  which  take  root 
and  soon  become  separate 
individuals.  This  latter 
method  is  often  more  cer, 
tain  than  reproduction  by 
seeds,  since  the  new  plant 
may  remain  attached  to 
the  old  one  until  estab- 
lished ;  and  some  species, 
such  as  the  potato  and 
horse-radish  of  our  gar- 
dens, and  the  sugar  cane 
and  sweet  potato,  have 
almost  abandoned  seeds  in 
favor  of  it.  In  most  cases, 
however,  seed  production 
and  vegetative  multipli- 
cation    proceed    side    by 

side,  one  being  used  for  multiplying  the  plant  in  a  particular 
station  and  the  other  for  spreading  it  into  other  regions. 

181 


Fig.  130.    A  lilac  shrub  that  has  pro- 
duced numerous  suckers 


182 


AGRONOMY 


Typical  forms  for  propagation.  The  branches  of  almost  any 
plant  may  strike  root  under  favorable  circumstances,  but  in 
plants  that  depend  very  much  upon  vegetative  methods  there 
are  usually  well-defined  parts  developed  for  the  work.  Several 
of  these  have  received  distinctive  names,  such  as  sucker,  stolon, 
offset,  tuber,  rootstock,  bulblet,  and  cormel.  A  snicker  ls  pro- 
duced by  an  adventitious  bud  upon  some  underground  part, 

usually  a  root.  Many 
plants,  among  which 
may  be  mentioned  the 
lilac,  plum,  locust,  and 
white  poplar,  sucker 
freely.  In  such  species 
injury  to  the  root  or 
cutting  back  the  top 
may  induce  suckering. 
A  stolo7i  is  a  slender 
branch  that  bends  over 
and  roots  at  the  tip,  as 
in  the  black  raspberry, 
currant,  June  berry, 
and  golden  bell.  The 
offset  is  a  short,  thick, 
horizontal  branch,  either 
on  the  surface  or  un- 
derground, which  pro- 
duces a  plant  at  the  tip.  It  differs  from  a  stolon  chiefly  in 
being  shorter  and  thicker  and  designed  solely  for  reproduction. 
The  century  plant,  house  leek,  and  ostrich  fern  produce  nu- 
merous offsets.  Runners  differ  from  offsets  mainly  in  being 
slenderer  and  longer,  and  in  producing  new  plants  at  each  node, 
as  in  the  strawberry.  Tubers  are  short,  much  thickened  under- 
ground branches  that  lie  in  the  soil  over  a  season  of  cold  or 
drought  and  produce  new  plants  upon  the  return  of  a  more 


I 


Fig.  131.    Base  of  a  sunflower  stem  showin: 
offsets  for  reproducing  the  plant 


PROPAGATION 


183 


favorable  season.   The  potato  and  artichoke  are  good  examples. 
RooUtocks  are  also  subterranean  stems,  but  differ  from  tubers 


Fig.  132.    Onion  bulbs 
The  sectioned  specimens  show  the  origin  of  bulblets 

in  being  the  main  axes  of  the  plants  instead  of  branches,  and 
in  living  much  longer.  When  the  rootstock  branches,  how- 
ever, these  shoots  act  exactly  like  tubers  in  forming  new 
plants.  The  iris  and  Solomon's  seal 
are  good  illustrations  of  rootstocks. 
Bulblets,  or  bulbils,  are  budlike  struc- 
tures, really  small  buds,  produced  in 
the  axils  of  bulb  scales,  as  in  many 
lilies  and  the  "  potato "  onion,  or  on 
the  aerial  parts  of  plants,  such  as 
may  be  seen  in  the  tiger  lily  and  the 
"  top "  onion.  Cormels  are  small  con- 
densed stems  with  one  or  more  buds, 
and  are  produced  by  corms,  such  as  the  gladiolus  and  crocus. 
Artificial  propagation.  In  multiplying  his  specimens  the 
gardener   takes   advantage  of  all  the  methods  evolved   by 


Fig.  133.  A  corm  of  gla- 
diolus with  several  small 
cormels  attached 


184 


AGRONOMY 


plants,  to  which  he  adds  various  others  which  careful  manip- 
ulation and  a  knowledge  of  plant  growth  make  possible. 
Often  injury  to  the  plant  will  cause  it  to  produce  parts 
designed  for  reproduction.  Cuts  near  the  base  of  bulbs  or 
corms  will  cause  bulblets  or  cormels  to  develop.  Even  bulb 
scales,  when  treated  as  softwood  cuttings,  may  develop  into 
new  plants.  All  vegetative  multiplication  depends  upon  a 
division  of  the  plant,  which  fact  may  be  made  use  of  in  many 
ways.  Cormels  and  bulblets  are  removed  from 
the  plant  and  treated  like  seeds.  Rootstocks 
are  separated  into  bits,  each  of  which  contains 
one  or  more  buds  and  a  few  roots.  Tubers, 
like  rootstocks,  are  cut  into  pieces,  a  single 
specimen  thus  producing  several  new  plants. 
Runners,  offsets,  stolons,  and  suckers  are  sep- 
arated from  the  parent  plant  and  set  where 
wanted.     Other    species,    such    as    the    phlox, 


^/ 


'i 


,v 


Fig.  134.    A  species  of  sunflower  {TIelianthus  laetiflorus)  showing  the 
evolution  of  a  tuber  from  an  offset 


golden  glow,  and  chrysanthemum,  which  grow  in  clumps  with- 
out well-defined  rootstocks  or  other  means  of  propagation, 
may  be  simply  cut  in  pieces  and  each  piece  planted  separately. 
Chief  among  the  artificial  methods  which  man  has  devised 
for  multiplying  plants  may  be  named  cuttings,  layering,  bud- 
ding, and  grafting. 

Cuttings.  Nearly  all  plants  may  be  increased  in  number  by 
detached  parts,  which,  placed  in  moist  sand  or  even  water, 
soon  strike  root  and  become  independent  individuals.  The 
"  slips  "  by  which  house  plants  are  commonly  propagated  are 


PROPAGATION 


185 


good  examples.  These  cuttings  are  placed  in  two  groups : 
green  or  softwood  cuttings,  made  mostly  from  herbaceous  plants 
and  intended  to  be  rooted  at  once ;  and  hardwood  cuttings, 
made  from  woody  plants  late  in  autumn.  The  latter  are  kept 
in  a  dormant  condition  through  the 
winter  and  are  rooted  the  following 
spring.  This  latter  form  of  cutting 
is  the  one  commonly  employed  in 
•multiplying  the  woody  plants,  but 
many  of  these  may  also  be  propa- 
gated by  softwood  cuttings,  espe- 
cially roses,  currants,  golden  bell, 
willow,  and  poplar.  For  this  pur- 
pose the  cuttings  should  be  taken 
while  the  wood  is  young  and  ten- 
der. In  making  any  kind  of  cut- 
ting it  is  desirable  that  the  cuts  be 
made  just  below  the  nodes,  since 
the  new  roots  usually  spring  from 
these  parts.  Among  the  plants  com- 
monly grown  from  softwood  cut- 
tings are  carnations,  geraniums, 
begonias,  cluysanthemums,  and 
those  specimens  known  as  "  foliage 
plants."  When  set,  about  one  third 
of  each  cutting  should  project  above 
the  soil.  To  prevent  loss  of  mois- 
ture while  they  are  making  roots,  it 
is  customary  to  remove  part  or  all 
the  leaves  before  setting  and  to  protect  them  from  the  drying 
effects  of  the  air  by  sheltering  with  glass  or  thin  cloth.  Plenty 
of  warmth  and  moisture  is  necessary  to  make  most  cuttings 
root  rapidly,  but  they  should  not  be  kept  so  close  as  to  pre- 
vent ventilation.   The  hardier  plants,  however,  will  root  if  the 


Fig.  135.    A  geranium  cutting 
wliich  has  struck  root 

From    Bergen    and    Caldwell's 
"  Practical  Botany  " 


186 


AGRONOMY 


cuttings  are  merely  stuck  in  moist  soil  in  a  shady  place. 
Several  forms  of  softwood  cuttings  have  distinctive  names. 
heaf  cuttings  are  made  from  leaves  or  parts  of  leaves,  which 
are  pegged  down  on  moist  sand  and  kept  close.    After  a  time 


Fig.  136.   A  Jamaican  fern  (Faydenia)  in  which 
the  leaves  form  new  plants  at  their  tips 

tiny  plants  will  begin  to  form  along  the  edge  of  the  leaves. 
Begonias,  wax  plants,  and  bryophyllums  are  multiplied  in  this 
way,  and  among  wild  plants  the  sundews  and  many  ferns  have 
the  same  faculty.  Stem  cuttings  are  the  ordinary  "  slips "  or 
twigs  taken  with  three,  or  more  joints.  Tuber  cuttings  are 
pieces  of  tubers  with  one  or  more  "  eyes,"  or  buds.    Cuttings 


PROPAGATION  187 

of  this  kind  are  the  customary  means  of  multiplying  potatoes, 
artichokes,  and  dahlias.  Root  cuttings  may  be  used  for  getting 
additional  plants  of  quince,  horse-radish,  blackberry,  sea  kale, 
phlox,  butterfly  weed,  and  the  like.  In  such  cases  adventitious 
buds  are  formed  on  the  roots,  although  they  do  not  normally 
occur  in  this  way.  In  the  case  of  phlox  and  butterfly  weed, 
however,  small  roots  left  in  the  soil  after  the  plant  is  dug  are 
almost  certain  to  send  up  new  plants,  and  in  horse-radish  and 
sea  kale  the  larger  roots  are  depended  upon  for  increasing 
the  number  of  plants.   Dandelion  roots  can  also  originate  buds 


Fig.  137.   Tubers  of  artichoke  {Helianthus)  and  potato,  which  are  usually 
propagated  by  tuber  cuttings 

in  this  way,  and  a  single  piece  of  root  left  in  digging  may  pro- 
duce several  new  plants.  Root  cuttings,  like  tuber  cuttings, 
are  entirely  covered  by  the  soil  when  planted. 

Hardwood  cuttings.  Hardwood  cuttings  are  made  from  ma- 
ture wood  not  more  than  two  years  old  and  usually  younger. 
They  are  cut  at  least  six  inches  long  and  are  taken  late  in 
autumn  when  the  wood  is  dormant.  They  are  not  set  until 
the  following  spring  and  must  be  kept  ui  a  cool  moist  place 
until  used.  In  common  practice  they  are  tied  in  bundles  of 
about  one  hundred  each  and  buried  a  foot  or  more  deep  and 
upside  down  in  a  well-drained  spot,  or  they  may  be  kept  in 
moist  sand  in  a  cool  cellar.  During  the  winter  a  tissue  called 
the  callus  forms  over  the  cut  ends,  and  from  this  or  near  it  the 
new  roots  start.  In  plants  that  root  rather  easily  the  cuttings 
are  often  set  out  in  autumn.  Nearly  all  our  trees,  shrubs,  and 
woody  vines  may  be  propagated  by  hardwood  cuttings,  though 
the  form  of  these  depends  somewhat  upon  the  species  it  is 


188 


AGRONOMY 


desired  to  multiply.  Besides  the  simple  cuttings  of  three  or 
more  joints,  there  are  dngle  eye  cuttinyB  consisting  of  a  single 
node  with  its  buds.  These  are  planted  in  the  soil,  usually  in 
the  greenhouse,  and  treated  as  if  they  were  seeds.  Heel  cut- 
tings are  made  by  removing  a  twig  with  part  of  the  old  wood 
attached  to  it,  the  latter  forming  the  "  heel."  Mallet  cuttinga 
are  sections  of  the  main  stem  with  the  twig  attached.    In 

some  species,  especially 
those  with  very  hard 
wood,  these  latter  root 
more  readily  than  the 
simple  stem  cuttings. 
In  general,  hardwood 
cuttings  should  be  set 
so  that  not  more  than 
one  bud  appears  above 
the  soil. 

Layering.  Layering 
is  a  modification  of  re- 
production by  cuttings 
used  with  plants  that  do 
not  readily  strike  root 
from  separate  pieces.  In 
this  method  the  twig  is 
induced  to  strike  root, 
while  still  attached  to 
the  parent  plant,  by  being  bent  down  and  covered  with  moist 
soil.  Often  the  branch  is  cut  part  way  through  where  it  is 
covered  with  soil,  or  it  may  be  bent  or  twisted,  or  a  layer  of 
bark  may  be  removed  to  further  influence  the  production  of 
roots.  The  black  raspberry,  hobblebush,  and  golden  bell  root 
naturally  at  the  tips,  and  other  plants  may  be  made  to  do  so. 
This  is  called  tip  layering  and  is  really  the  forming  of  an  arti- 
ficial stolon.   In  vine  layering  the  branch  may  be  covered  with 


Fig.  138.   Three  forms  of  hardwood  cuttings 

On  the  left,  the  ordinary  form ;  in  the  middle,  a 
heel  cutting ;  on  the  right,  a  mallet  cutting 


PROPAGATION  189 

soil  at  several  points,  and  when  these  form  roots,  they  are  cut 
up  into  separate  plants.  Grapes,  honeysuckles,  wistaria,  and 
many  others  may  be  propagated  thus.  Branches  that  rise 
from  the  base  of  shrubs  often  form  roots  and  may  be  removed 
to  form  new  plants.  This  process  is  often  hastened  by  the 
grower,  who  first  cuts  back  the  plant  to  make  it  throw  up 
numerous  shoots  and  then  heaps  the  soil  up  ait)und  them  so 
that  they  will  root.  This  is  known  as  mound  layering.  What 
is  essentially  a  form  of  layering  may  be  often  seen  in  green- 
houses where  various  tropical  species,  such  as  the  rubber  plant, 
are  multiplied  by  tying  a  ball  of  wet  moss  about  a  branch  near 
the  tip,  first  injuring  the  bark  to  make  it  root  at  that  point. 
The  moss  is  kept  wet  and  in  due  time  is  filled  with  roots,  after 
which  the  branch  is  cut  off.  This  is  called  air  layering  or  pot 
layering. 

The  sand  box.  Although  established  plants  thrive  only  in 
rich  soil,  cuttings  root  better  in  clean,  sharp  sand.  The  willow, 
wandering  Jew,  and  nasturtium  root  readily  in  water.  The 
nurseryman  roots  his  cuttings  in  beds  of  moist  sand  in  the 
greenhouse,  but  for  home  work  a  box  of  sand  set  in  a  shady 
place  and  covered  with  glass  or  thin  cloth  is  very  useful. 
Care  should  be  taken  to  see  that  the  sand  is  free  from  inju- 
rious fungi  and  insects,  and  after  being  used  for  one  lot  of 
cuttings  should  be  sterilized  by  baking  or  pouring  boiling 
water  through  it  before  it  is  used  for  another.  The  cuttings 
should  be  given  a  warm  and  even  temperature  and  should 
not  be  allowed  to  suffer  for  water  or  fresh  air. 

Budding.  Budding  does  not  increase  the  number  of  plants, 
but  it  may  be  employed  to  increase  the  number  of  a  certain 
kind.  It  is  really  a  form  of  transplanting  whereby  the  bud  of 
a  desirable  species  is  made  to  grow  upon  one  less  desirable 
and  thus  change  the  nature  of  the  plant.  It  is  used  for  mak- 
ing worthless  species  productive,  for  multiplying  forms  that 
will  not  come  true  from  seeds,  and  for  hastening  the  fruiting 


190 


AGRONOMY 


% 


of  others.  All  of  our  superior  fruits  and  many  of  our  nut 
trees  are  budded  or  grafted  upon  other  stock  because  their 
characters  are  not  fixed  in  the  seed.  Having  one  good  plant, 
however,  we  may  make  as  many  others  as  we  choose  by  bud- 
ding. In  this  process  it  makes  no  difference  if  the  fruits  pro- 
duced by  the  stock  are  worthless.  The  bud  will  form  a  new 
crown  that  will  produce  fruits  like  the  plant  from  which  it 
was  taken.  In  growing  the  stocks,  therefore, 
seeds  from  any  source  may  be  sown.  The 
plants  are  budded  when  one  or  two  years 
old,  and  thereafter  have  all  the  character- 
istics of  the  superior  strain.  Usually  only 
closely  related  forms  can  be  budded  success- 
fully. The  plants  most  frequently  treated  in 
this  way  are  the  stone  fruits,  nut  trees,  and 
some  of  the  citrous  fruits.  Budding  is  per- 
formed in  late  June,  July,  August,  and  early 
September. 

Method  of  budding.  In  the  common  form 
of  budding  a  T-shaped  cut  is  made  in  the 
bark  of  the  stock,  the  upper  edges  of  the  cut 
are  carefully  turned  back,  and  a  new  bud 
with  more  or  less  bark  attached  is  inserted, 
after  which  the  bark  of  the  stock  is  pressed 
into  place  and  tied  for  a  week  or  more  until 
the  bud  has  grown  fast.  The  cut  in  the  stock 
should  go  halfway  around  the  twig  or  stem,  and  the  cut  at 
right  angles  to  it  should  be  about  an  inch  and  a  half  long. 
Both  should  extend  inward  as  far  as  the  new  wood.  The 
bud  should  be  selected  from  a  vigorous  and  healthy  plant, 
and  removed  with  an  upward  cut  of  a  sharp  knife,  beginning 
a  quarter  of  an  inch  below  the  bud  and  ending  the  same  dis- 
tance above  it.  The  cut  should  be  made  just  deep  enough  to 
remove  a  thin  shaving  of  the  new  wood,  which  may  afterwards 


Fig.  139.    A  twig 

with  buds  removed 

for  budding 


PKOPAGATION 


191 


be  removed  with  the  knife,  or,  if  very  thin,  it  may  be  inserted 
with  the  bud.  The  leaf  that  occurs  below  each  bud  may  be 
severed  where  the  blade  joins  the  petiole,  and  the  latter  left 
for  a  handle.  The  bud  and  the  bark  removed  with  it  should 
be  inserted  in  the  cleft  in  the  stock  and  care  taken  to  see  that 
the  cambium  of  bud  and  stock  are  in  contact.  The  bark  of  the 
stock  should  be  tied  securely  about  the  bud  with  two  or  three 
turns  of  twme  or  waxed  cotton,  but  the  bud  itself  must  not 
be  covered,  and  as 
soon  as  it  has  been 
incorporated  with 
the  stock,  which 
should  occur  in 
about  ten  days,  the 
wrappings  must  be 
removed.  The  bud 
remains  dormant 
until  spring,  and 
as  soon  as  growth 
begins,  the  part  of 
the  stock  above 
the  bud  should  be 
removed  and  the 
latter  left  to  form 

the  new  plant.  In  budding  young  plants  the  bud  is  inserted 
about  two  inches  above  the  soil ;  in  larger  specimens  it  may  be 
inserted  anywhere  on  the  young  growth.  By  selecting  buds 
of  different  varieties  one  may  have  several  kinds  of  fruit  on 
the  same  tree.  While  budding,  neither  bud  nor  stock  should 
be  allowed  to  become  dry.  It  is  also  well  to  bud  on  the  north 
side  of  the  stock,  where  the  bud  will  not  be  exposed  to  the 
sun.  Several  other  forms  of  budding  are  in  use,  but  the  prin- 
ciple is  the  same  in  all.  In  ring,  Jlute,  or  annular  budding  a 
piece  of  bark  extending  part  way  around  the  stock  is  removed 


Fig.  140.   Three  stages  in  the  operation  of  budding 
In  the  figure  on  the  right  the  work  has  been  completed 


192  AGRONOMY 

and  a  similar  piece  of  bark  with  a  bud  from  another  plant  is 
fitted  in.  This  method  is  most  frequently  used  in  budding 
thick-barked  trees  such  as  hickory  and  magnolia,  the  work 
being  performed  in  early  spring.  Prong  budding  is  really  a 
form  of  grafting  in  which  a  short  twig  is  treated  as  a  bud. 

Grafting.  Grafting  is  in  many  respects  like  budding,  since 
it  consists  in  transferring  a  part  of  one  plant  to  another,  but 
in  the  present  case  a  small  twig,  called  a  don,  or  graft,  is  used 
instead  of  a  bud.  The  cions  are  collected  and  stored  in  autumn 
exactly  like  hardwood  cuttings,  and  the  only  practical  differ- 
ence between  them  is  that  the  cutting  is  designed  to  draw 
part  of  its  nourishment  from  the  soil  through  its  own  roots, 
while  the  cion  is  intended  to  become  a  part  of  another  plant 
with  no  roots  of  its  own.  The  essential  thing  in  all  grafting 
is  to  see  that  the  cambium  of  stock  and  cion  meet,  and  that 
the  point  where  they  join  is  protected  by  grafting  wax  until 
the  two  have  grown  together.  Grafting  must  be  done  in  late 
winter  or  early  spring  while  both  stock  and  cion  are  dormant. 
As  in  budding,  cion  and  stock  must  be  from  nearly  allied 
species.  Sour  apples  or  pears  may  grow  on  sweet-apple  stock 
and  peaches  on  plum  stock,  but  widely  separated  species  can 
seldom,  if  ever,  be  made  to  unite.  A  single  tree  may  be  made 
to  bear  half  a  hundred  different  varieties  of  apples  by  graft- 
ing, and  each  will  come  true  to  its  nature.  In  species  with 
dioecious  flowers  grafting  may  be  employed  to  make  sterile 
forms  fertile. 

Different  forms  of  grafting.  Two  principal  forms  of  grafting 
may  be  distinguished :  cleft  grafting  used  in  working  over  old 
trees ;  and  wliip  grafting,  the  method  commonly  employed  with 
small  or  young  stock.  In  cleft  grafting,  a  branch  about  two 
inches  thick  is  sawed  off,  the  stump  is  split  with  a  chisel  or 
knife,  and  the  base  of  the  cion,  cut  to  slender  wedge  shape, 
is  inserted  in  the  cleft.  Usually  two  cions  are  used,  one  on 
each  side  of  the  cleft,  and  to  insure  that  the  cambiums  of 


PKOPAGATION 


193 


stock  and  cion  shall  meet,  the  cions  are  often  made  to  diverge 

slightly.  The  cleft  is  then  covered  thoroughly  with  grafting 
wax,  to  keep  out  insects  and  decay 
until  the  wound  heals.  Crown  grafting 
is  like  cleft  grafting  except  that  it  is 
used  in  renewing  the  top  of  shrubs 
and  vines  that  have  been  cut  off  at 
the  surface  of  the  soil.  Cleft  grafting 
is  rarely  used  except  in  attempts  to 
give  old  trees  a  new  lease  of  life.  For 
all  ordinary  work  whip  grafting  is  em- 
ployed. Numerous  forms  of  this  are  in 
use,  but  they  differ  for  the  most  part 
only  in  the  way  cion  and  stock  are 
jomed.  In  the  form  called  saddle  graft- 
ing the  top  of  the  stock  is  cut  in  wedge 
shape  and  the  cion  is  cut  with  a  deep 
notch  to  match  it.  In  splice  grafting 
a  long  tapering  cut  from  one  side  of 

the  stock  to  the  other  fits  a  similar  cut  on  the  cion.    Tongue 

grafting  is  an  improved  form  of  splice 

grafting,  in  which  a  longitudinal  cut  is 

made  about   one  third  of  the  distance 

from  the  tip  of  the  cut  in  both  cion  and 

stock.  These  are  then  wedged  together, 

forming  a  close  union  that  is  not  readily 

injured  by  the  weather.  In  veneer  graft- 
ing a  notch  is  made  through  the  bark  of 

the  stock,  and  the  base  of  the  cion,  cut 

to  fit,   is    inserted.     Bridge  grafting  is 

sometimes  employed  to  repair  injuries 

to  the  bark  of  large  trees.    The  edges 

of  the  wound  are  first  straightened  up  and  several  twigs  of 

the  same  species  are  obtained,  their  ends  cut  wedge  shape 


Fig.  141,     Cleft  grafting 

This    method    is    used    on 
large  specimens 


^' 


Fig.  142.  Three  forms  of 
whip  grafting 


194 


AGRONOMY 


and  inserted  into  the  bark  above  and  below  the  wound.  In 
this  way  the  sap  is  carried  past  the  injury  until  the  tree  can 
cover  it  with  bark.  In  root  grafting  the  cion  is  joined  to  a 
piece  of  root.  Tliis  is  regarded  as  one  of  the  best  forms  of 
grafting,  since  the  cion  may  also  put  out  roots  and  help  to 
nourish  the  plant;  in  fact,  this  hardly  differs  from  growing 

a  plant  from  a  hardwood  cut- 
ting. In  all  the  forms  of  whip 
grafting,  stock  and  cion  are 
carefully  bound  together  with 
waxed  cotton  twine  or  graft- 
ing wax  until  a  perfect  union 
occurs.  Root  grafts,  being  un- 
derground, do  not  need  this 
protection. 

Although  herbaceous  plants 
are  rarely  grafted,  it  can  be 
accomplished.  Grafts  between 
the  tomato  and  the  potato,  the 
morning-glory  and  the  sweet 
potato,  the  artichoke  and  the 
sunflower,  are  now  and  then 
reported.  In  grafting  herba- 
ceous plants  veneer  grafting 
is  the  best  form  to  use,  but 
in  this  case  the  cut  in  the 
stock  should  be  made  deeper 
Even  fruits  have  been  grafted 
when  half  grown.  The  grafting  of  soft-wooded  plants  is  most 
successful  when  carried  on  under  glass,  where  the  conditions 
of  temperature  and  moisture  can  be  controlled. 

Inarching.  Inarching  is  a  form  of  grafting  in  which  cion  and 
stock  are  united  while  both  are  still  joined  to  their  own  roots. 
In  this,  one  stem  is  bent  over  toward  the  other,  the  cambium 


Fig.  143.   Tongue  grafting 
Illustration  of  one  of  the  best  methods 

than  for  hard-wooded  plants. 


PROPAGATION  195 

of  each  exposed,  and  the  two  stems  bound  together  until  a 
union  is  formed.  The  top  of  the  stock  is  now  cut  off  and  the 
cion  cut  away  from  its  roots.  In  the  same  way  a  small  plant 
in  a  pot  may  be  inarched  to  the  branches  of  a  large  tree.  In 
the  forest  one  may  often  see  examples  of  natural  inarching 
where  two  plants  have  come  into  contact. 

Grafting  wax.  To  make  grafting  wax,  take  four  parts  of 
rosin,  two  parts  of  beeswax,  and  one  part  of  tallow  or  Imseed 
oil,  and  melt  all  together.  When  thoroughly  mixed  pour  into 
cold  water,  and,  when  cool  enough,  work  it  like  molasses  candy 
until  it  assumes  a  light  straw  color.  Make  into  rolls  and  wrap 
in  waxed  paper  until  wanted.  If  a  harder  wax  is  desired,  the 
amount  of  rosin  or  beeswax  may  be  increased.  The  hands 
should  be  greased  with  tallow  before  attempting  to  work  the 
wax.  Waxed  twine  for  tying  buds  and  grafts  may  be  prepared 
by  putting  a  ball  of  No.  18  knitting  cotton  in  the  kettle  of 
melted  wax  for  a  few  minutes. 

Effect  of  stock  on  cion.  Usually  the  nature  of  the  stock  has 
little  effect  on  the  cion,  but  cases  are  known  in  which  apples 
grafted  on  wild-crab  stock  have  produced  more  acid  fruits, 
while  late  apples  may  ripen  earlier  as  a  result  of  grafting 
them  on  stocks  of  earlier  varieties.  Certain  species  may  be 
dwarfed  by  grafting  them  on  slow-growing  stock,  and  the 
time  of  fruiting  may  often  be  greatly  modified  by  the  kind  of 
stock  and  cion  selected.  Apples  usually  grow  for  ten  or  more 
years  before  fruiting,  but  a  young  seedling  grafted  on  old 
stock  may  fruit  in  a  year  or  two.  On  the  other  hand,  a  twig 
from  an  old  tree  grafted  upon  a  seedling  may  grow  for  years 
before  producing  fruit.  Many  French  grapes  are  grafted  on 
American  stocks,  which  are  more  resistant  to  the  dreaded 
plant  louse,  Phylloxera,  which  infests  the  roots.  Rarely  the 
union  of  graft  and  stock  may  produce  twigs  with  characters 
that  appear  intermediate  between  the  two.  Such  specimens 
are  known  as  graft  hybrids. 


196  AGKONOMY 

PRACTICAL  EXERCISES 

1.  From  pictures,  from  dried  specimens,  and  from  jjlants  in  the  gar- 
den, learn  to  recognize  the  various  forms  by  which  plants  are  propagated 
vegetatively. 

2.  In  the  school  garden  examine  all  the  crops  grown,  with  a  view 
to  propagating  them.  Which  are  most  susceptible  to  treatment  in  this 
way,  the  crop  plants  or  the  permanent  species?  Can  you  discover  the 
reason  for  the  difference  ? 

3.  In  the  borders  find  plants  to  illustrate  propagation  by  each  of 
the  methods  given  in  this  book.    Make  a  list  of  them. 

4.  Make  softwood  cuttings  and  root  them  in  the  hotbed  or  cold 
frame. 

5.  In  autumn  make  hardwood  cuttings  of  all  the  tyi>es  mentioned, 
and  store  as  required.  In  spring,  if  cuttings  of  this  kind  have  been  left 
by  a  former  class,  try  rooting  them  in  the  cold  frame,  in  the  hot  bed,  or 
in  the  open. 

6.  Layer  any  vine  that  may  be  convenient  in  the  school  garden. 
Try  layering  currant  bushes  for  planting  later  at  home. 

7.  If  cions  are  at  hand  in  time  to  graft,  make  several  kinds  of  whip 
grafts.  If  materials  for  practical  grafting  are  not  at  hand,  make  grafts 
of  any  twigs  for  practice. 

8.  Plant  seeds  of  different  trees  in  the  exi)eriment  plots,  for  use  of 
the  next  class  in  budding  and  grafting. 

9.  Bud  a  convenient  plum  or  peach  tree.  Each  class  should  plant 
seeds  to  produce  young  trees  for  this  purpose  for  the  next  class.  If  your 
budding  ojjeration  is  successful,  take  the  plant  home  and  set  it  out. 

10.  If  a  large  peach  or  plum  tree  is  available,  set  in  it  buds  from 
other  trees  bearing  different  kinds  of  the  same  fruit.  One  may  have 
specimens  of  all  the  kinds  in  the  neighborhood  by  this  method. 

11.  Make  grafting  wax  and  carry  some  home  for  use  in  your  own 
grounds. 

References 

Bailey,  "Manual  of  Gardening." 
Goff,  "  Principles  of  Plant  Culture." 

Farmers'  Bulletins 

1.57.   The  Propagation  of  Plants. 

408.    School  Exercises  in  Plant  Production. 


CHAPTER  XIV 

DECORATIVE  PLANTING 

Purpose.  The  purpose  of  decorative  planting  is  to  add  to 
the  comfort  and  attractiveness  of  our  surroundmgs  by  plant- 
ing those  plants  that  are  conspicuous  either  for  the  beauty  of 
their  flowers,  the  color  and  cutting  of  their  foliage,  or  the 
symmetry  of  their  form,  thus  making  homes  of  houses  and 
parks  of  wildernesses.  Not  all  planting  of  this  kind,  liow- 
ever,  can  be  called  decorative.  To  be  entitled  to  the  name  it 
must  proceed  along  definite  lines,  with  a  preconceived  design 
in  mind ;  for  unless  a  definite  plan  is  adhered  to,  the  result  is 
likely  to  be  lacking  in  harmony  and  coherence.  In  planting  the 
home  grounds  the  aim  should  be  to  set  off  the  house  to  the 
best  advantage,  emphasizing  the  good  points  and  concealing 
the  poor  ones ;  in  short,  to  make  a  picture,  with  the  house  as 
the  central  figure  and  the  borders  as  the  frame. 

Lawn  making.  Few  things  add  more  to  the  beauty  of  the 
home  grounds  than  a  broad  expanse  of  well-kept  lawn,  but 
this  can  be  produced  only  by  proper  care  in  the  making.  If 
the  old  lawn  is  unsatisfactory,  it  is  best  to  spade  or  plow  it  up 
in  late  fall  or  early  spring  and  start  a  new  one.  The  first 
step  in  lawn  making  is  to  see  that  the  land  is  properly  drained. 
If  it  is  not,  this  should  be  taken  care  of  by  one  or  more  lines 
of  tile  drain.  After  digging,  the  soil  should  be  very  thor- 
oughly worked  over  until  it  is  well  pulverized  and  carefully 
leveled.  If  the  soil  is  lacking  in  fertility,  a  quantity  of  well- 
rotted  manure  should  be  worked  into  it,  or  other  fertilizers 
applied.  Small  lawns  should  be  perfectly  level  unless  the 
residence  is  on  sloping  ground.    In  the  latter  case  it  is  much 

197 


198 


AGRONOMY 


better  to  have  the  lawn  slope  gently  away  from  the  house 
than  to  cut  it  up  by  banks  and  terraces,  since  every  divi- 
sion, whether  by  path  or  terrace,  tends  to  make  it  look 
smaller   than    it  really  is.    If   terraces    cannot   be  avoided, 

they  are  best  placed 
near  the  house,  where 
they  may  become,  in  a 
measure,  a  part  of  the 
building,  or  else  as 
far  away  as  possible 
—  at  the  street  line  or 
on  the  borders  of  the 
property.  On  no  ac- 
count should  the  center 
of  the  small  la^vn  be 
lower  than  the  borders, 
since  a  concave  surface 
tends  to  make  distances 
appear  shorter  and  the 
lawn,  in  consequence, 
smaller.  A  slightly  con- 
vex surface,  on  the 
other  hand,  gives  a 
more  spacious  look  to 
the  property,  and  in 
large  lawns  the  center 
is  often  raised  slightly 
to  prevent  it  from  look- 
ing hollow  at  this  point. 
Since  the  grasses  are 
cool-weather  plants  and  flag  during  the  summer,  it  is  best  to 
seed  the  lawn  in  late  fall  or  early  spring,  so  that  the  plants 
may  become  established  before  the  hot  weather  sets  in.  If 
seeded  later,  care  should  be  taken  that  the  young  plants  do 


1 

-4 

|f 

< ' .         i 

Fig.  144.    Hickory  Creek  at  Joliet,  Illinois 

An  illustration  of  the  way  Nature  arranges  her 
trees  and  shrubs 


DECORATIVE  PLANTING 


199 


not  suffer  from  drought.  Bare  spots  in  an  old  lawn  can  be 
loosened  with  a  rake  and  reseeded  at  any  time.  Occasionally 
when  a  lawn  is  wanted  quickly,  or  the  soil  on  a  sloping  bank 
is  to  be  retained,  the  whole  area  may  be  sodded.  For  this 
work  sods  from  an  old  pasture  are  best,  since  they  consist  of 
only  the  most  resistant  grasses  and  are  fairly  free  from  weeds. 
Ground  to  be  sodded  should  be  prepared  as  carefully  as  for 
seeding.    After  the  sods  are  laid  they  should  be  thoroughly 


Fig.  145.   Forest  and  stream  illustrating  Nature's  method  of  planting 

watered  and  then  beaten  into  place  with  the  back  of  a  spade 
or  rolled  with  a  heavy  roller.  It  is  difficult  to  make  grass 
grow  in  deep  shade,  under  evergreen  trees  and  the  like,  and 
some  other  ground  cover  is  often  used.  Among  the  best 
plants  for  this  purpose  are  the  periwinkle  or  myrtle,  lily  of 
the  valley,  and  moneywort. 

Paths  and  lawn  planting.  In  small  lawns  the  paths  should 
be  straight  and  direct,  but  in  larger  areas  they  may  curve, 
especially  if  the  surface  of  the  land  is  uneven.  Every  path  or 
drive  crossing  the  lawn  makes  it  look  smaller  and  adds  to  the 
care  that  must  be  bestowed  upon  it ;  no  unnecessary  walk, 


200 


AGRONOMY 


therefore,  should  be  permitted.  Paths  and  drives  are  often 
sunk  a  few  inches  below  the  surface  of  the  lawn,  which  thus 
conceals  or  renders  them  less  conspicuous  and  contributes  to 
the  appearance  of  spaciousness  so  desirable  to  maintain.  For 
the  same  reason  the  center  of  the  lawn  should  be  kept  open 
and  free  from  flower  beds,  shrubs,  and  trees.  In  large  grounds, 
and  in  strictly  formal  plantmg,  such  things  may  be  allowed, 
but  they  are  out  of  place  on  the  home  grounds.    The  kettles. 


iB^^^^^^^^^I 

■ 

Ml 

m 

^J|::|tjff 

M  i 

v.,     ■■;''§ 

A' 

Photograph  by  Waii;iier  I'ark  Conservatories,  Sidney,  Ohio 

Fig.  140.   A  corner  planted  in  the  natural  style 

vases,  sections  of  sewer  pipe,  paint  buckets,  and  tubs  filled 
with  flowers  that  are  often  seen  on  lawns  are  in  bad  taste  and 
should  not  be  tolerated.  Such  objects,  when  used  at  all,  should 
be  restricted  to  formal  planting.  Occasionally  it  is  desired  to 
separate  the  lawn  from  adjoining  fields  without  seeming  to 
do  so.  This  can  be  accomplished  by  digging  a  ditch  deep 
enough  to  conceal  a  fence  placed  in  the  bottom.  The  side  of 
the  ditch  nearer  the  house  may  be  slightly  raised,  thus  hiding 
the  ditch  and  making  the  lawn  appear  to  merge  into  the 
fields  beyond. 


DECORATIVE  PLAls^TIKG  201 

Care  of  the  lawn.  The  care  of  a  well-established  lawn  con- 
sists in  cutting,  fertilizing,  watering,  and  rolling  it.  It  should 
be  cut  frequently,  and  if  this  is  done,  the  clippings  may  be 
left  to  form  a  mulch  for  the  grass  roots  and  to  prevent  the 
seeds  of  weeds  from  becoming  established.  Cutting  the  lawn 
is  most  easily  done  in  the  morning,  since  at  this  time  the  cells 
of  the  grass  are  distended  with  water  and  therefore  more 
brittle.  The  lawn  should  be  watered  only  when  in  need  of  it, 
and  then  it  should  be  thoroughly  soaked.  An  occasional  heavy 
watering  is  much  to  be  preferred  to  the  daily  sprinkling  that  is 
often  given  it.  The  latter  causes  the  surface  to  bake,  and 
makes  the  grass  more  shallow-rooted  and  more  easily  burned 
up  in  summer.  Commercial  fertilizers  are  best  for  the  lawn ; 
the  winter  dressing  of  stable  manure  so  often  applied  is  not 
only  unsightly  and  unsanitary,  but  it  may  introduce  many 
noxious  weeds  from  seeds  mixed  with  the  manure.  Late  in 
the  season  the  grass  may  be  allowed  to  grow  longer  and  form 
a  cover  for  the  roots  during  winter.  In  early  spring  the  lawn 
should  be  carefully  raked  and  then  rolled  with  a  lieavy  roller, 
to  settle  back  into  place  any  grass  roots  that  may  have  been 
lifted  by  the  frost. 

The  border.  The  shrubs  and  flowering  plants  that  so  often 
find  a  place  on  the  lawn  are  better  located  on  its  borders.  Here 
they  add  a  distinct  note  to  the  ornamentation  of  the  grounds. 
Shrubs  and  flower  beds  scattered  over  the  lawn  give  it  a  spotty 
appearance,  out  of  all  harmony  with  the  rest  of  the  picture. 
Nor  should  flowering  plants  designed  for  cutting  be  allowed 
anywhere  on  the  lawn  or  in  the  borders.  They  are  best  re- 
stricted to  some  part  of  the  garden  where  the  loss  of  their 
blossoms  will  not  be  so  much  noticed.  The  flowering  plants 
in  the  borders  should  be  allowed  to  finish  their  season  of 
bloom  undisturbed.  In  planting  the  border  it  should  be 
remembered  that  Nature  always  works  in  curves,  and  if  an 
appearance  of  naturalness  is  to  be  produced,  straight  lines 


202 


AGRONOMY 


should  be  avoided.  The  line  where  lawn  and  border  meet 
should  be  a  series  of  graceful  curves,  and  the  slmibs  and 
herbaceous  plants  should  be  arranged  in  u-regular  groups. 
In  this,  one  can  have  no  better  guide  than  Nature  herself, 
and  a  visit  to  the  bushy  margins  of  an  old  field  or  the  edge 
of  a  woodland  will  be  of  great  assistance  to  the  observant 
student.  In  making  the  outline  of  the  border  a  stout  rope 
or  the  garden  hose  may  be  used  to  get  the  desired  curved 
effect,  and  the  line  can  then  be  marked  out  along  this. 

Arrangement  of  the  plants.    Trees,  shrubs,  vines,  and  her- 
baceous plants  may  all  find  appropriate  locations  in  the  border. 


Fig.  147.     The  wrong  way  to 
plant  shrubs  on  a  lawn 

Such    an   arrangement    makes   a 
spotty  appearance 


Fig.   148.    The  correct  way  to 
plant  a  lawn 

Shrubs  arranged  on  the  borders; 
center  of  the  lawn  kept  open 


The  trees  and  shrubs  are  used  to  form  the  framework  of  the 
plan,  and  the  less  rugged  and  assertive  plants  are  grouped 
about  them.  In  arranging  them  care  must  be  taken  that  the 
taller  specimens  do  not  shut  out  the  view  from  the  windows 
and  veranda  of  the  house.  In  large  grounds,  especially,  vistas 
to  distant  points  in  many  directions  should  be  maintamed. 
Grounds  that  have  been  planted  for  some  time  often  have 
these  views  obscured  by  an  undue  growth  of  shrubbery  un- 
less it  is  properly  trimmed.  On  the  other  hand,  undesirable 
views  or  unsightly  objects  can  be  entirely  concealed  from 


DECORATIVE  PLANTING 


203 


Fig.  149.    Slirubs  in  the  curves  of 
a  drive 


view  by  screens  of  shrubbery  planted  for  the  purpose.  A  pro- 
fusion of  low-growing  shrubs  should  be  used  to  conceal  the 
foundations  of  the  house,  and  vines  may  be  trained  over  walls 

and  pillars,  thus  carrying  the 
green  of  the  lawn  upward 
and  making  the  house  appear 
more  a  part  of  the  landscape. 
Shrubs  should  rarely  be  planted 
singly.  Their  beauty  is  greatly 
enhanced  if  several  are  set  to 
form  an  irregular  group,  but 
care  must  be  taken  to  allow 
for  future  growth,  else  they 
will  soon  begin  to  crowd  one 
another  and  fail  of  their  best 
development.  Not  only  should 
the  line  where  lawn  and  border  meet  be  irregular,  but  the  sky 
line  should  partake  of  the  same  character.  This  is  brought 
about  by  alternating  groups  of  tall  and  shorter  shrubs  and 
trees.  It  is  desirable,  also,  to  bring 
some  of  the  shrubs  out  toward 
the  margin  of  the  lawn,  forming 
recesses  or  bays  between  them  in 
which  herbaceous  plants  may  be 
grown.  Shrubs  may  be  planted  on 
the  concave  side  of  all  curves  in 
paths  and  drives,  thus  seeming  to 
give  a  reason  for  the  curve  as  well 
as  adding  to  the  spacious  appear- 
ance of  the  grounds  by  preventing 

all  parts  being  seen  at  once.  At  the  angles  where  paths 
intersect,  and  where  "  short  cuts "  are  likely  to  be  made,  it 
is  well  to  plant  thorny  shrubs  like  the  barberry,  locust,  and 
prickly  ash.    Such  plantings  are  also  frequently  made  in  the 


Fig.  150.  A  corner  planting 


204 


AGRONOMY 


front  of  shrubbery  where  it  borders  the  street,  to  prevent  the 
encroachment  of  the  pubhc. 

Shrubs  for  winter  effects.  The  best-planted  grounds  are  not 
designed  solely  for  their  beauty  in  summer.  A  proper  selection 
of  slu-ubbery  will  not  only  look  well  in  summer  but  will  add 
numerous  pleasing  tints  to  the  winter  landscape  and  brighten 
the  borders  with  the  colors  of  a  milder  season.  In  this  class 
are  the  bright  scarlets  and  purples  of  the  dogwoods  and  some 
willows  and  wild  roses,  the  yellow  and  gray  of  willow  and 
beech,  the  green  of  euonymus  and  cat  brier,  and  the  white 

of  the  birch  and  button- 
wood.  At  the  leafless 
season,  also,  the  form 
of  the  plant  is  thrown 
into  strong  relief,  and 
various  species  may  be 
planted  for  the  pictur- 
esque note  they  add  to 
the  winter  landscape. 
Among  common  species 
desirable  for  this  pur- 
pose are  the  hawthorns, 
the  river  birch,  black 
gum,  and  Lombardy  poplar.  Numerous  shrubs  produce  at- 
tractive fruits  that  persist  far  into  the  winter,  supplymg  food 
for  the  winter  birds  and  adding  a  touch  of  color  to  the  thick- 
ets. The  winterberry,  greenbrier,  bittersweet,  burning  bush, 
and  the  roses  are  good  for  this  purpose. 

Naming  the  shrubs  and  trees.  Slirubs  and  trees  are  among 
tlie  most  permanent  of  living  things  and  often  outlast  the 
works  of  man  himself.  It  is  desirable,  therefore,  that  the 
student  become  acquainted  with  those  commonly  planted, 
either  by  identifying  them  by  the  use  of  a  botanical  manual, 
which  is  much  the  better  way,  or  by  visiting  named  collections 


n 


Fig.  151.  Method  of  planting  a  corner  lot, 
to  prevent  paths  being  made  across  it 


DECORATIVE  PLANTING 


205 


in  parks,  botanical  gardens,  and  private  grounds.  The  more 
permanent  of  the  herbaceous  perennials  may  also  be  identified. 
Complete  lists  of  these,  with  notes  on  the  qualities  that  make 
them  desirable  for  planting,  may  be  obtained  from  the  nearest 
nursery  company.  A  large  number  of  the  more  desirable  are 
natives  of  our  own  fields  and  woods,  and  the  person  inter- 
ested in  decorating  his  grounds  will  find  many  of  them  ready 
to  his  hand  in  the  nearest  woodland  or  thicket.  Few  exotic 
species  surpass  our 
native  elders,  sumacs, 
dogwoods,  viburnums, 
wild  crabs,  currants, 
and  gooseberries  for 
decorative  planting. 
Trees  and  shrubs  with 
variegated  foliage  are 
usually  less  hardy  than 
those  with  green  leaves 
and  are  seldom  satis- 
factory in  the  home 
grounds. 

Herbaceous  plants. 
Herbaceous  plants  may 
be   considered  in  two 

groups,  the  annuals  and  the  perennials.  The  annuals  are  fre- 
quently desirable  for  quickly  covering  bare  spaces  and  for 
giving  an  abundance  of  bloom,  but  they  require  to  be  planted 
anew  each  year,  and  for  most  purposes  perennials  are  more 
desirable.  Some  of  the  most  showy  flowers,  however,  are  an- 
nuals. We  could  ill  spare  such  species  as  morning-glory, 
four-o'clock,  nicotiana,  nasturtium,  sweet  pea,  petunia,  aster, 
cosmos,  salvia,  and  verbena,  but  the  best  place  for  most  of  them 
is  in  the  flower  garden  where  their  beauty  may  be  admired  and 
the  flowers  removed  without  injuring  the  appearance  of  the 


Fig.  152. 


An  artificial  pond  planted  witli 
lotus  and  water  lilies 


206 


AGRONOMY 


surroundings.  Many  of  the  perennial  species  are  desirable  for 
the  flowers  they  produce,  but  when  these  are  needed  for  cut- 
thig,  they  too  should  be  planted  in  the  flower  garden  and  not 
in  the  border.  Among  the  better-known  perennials  are  the 
lilies,  columbines,  irises,  phloxes,  peonies,  sunflowers,  bell- 
worts,  bleeding  hearts,  and  pinks.  Left  to  themselves,  the 
herbaceous  perennials  soon  form  large  clumps,  which  may 
often  be  divided  and  used  to  make  further  plantings. 


Photograph  by  O.L.  Jordau 

Fig.  153.   An  old  planting  in  which  the  border  has  all  the  appearance  of  a 

natural  growth 

Arrangement  of  herbaceous  perennials.  In  planting  the  her- 
baceous perennials  the  general  rules  for  planting  shrubbery 
may  be  followed,  especially  those  regarding  mass  plantmg  and 
the  avoidance  of  straight  lines.  Since  they  are  always  planted 
for  the  decorative  effect  of  their  flowers,  they  should  be  placed 
in  front  of  the  shrubbery,  which  thus  forms  a  natural  back- 
ground and  renders  the  flowers  more  conspicuous.  Tall  plants 
should  be  placed  in  the  rear  and  successively  smaller  ones 


DECORATIVE  PLAi^TING  207 

should  cany  the  belt  of  verdure  down  to  meet  the  lawn.  A 
general  group  of  perennials  may  consist  of  several  sorts  inter- 
mixed, and  if  care  is  taken  to  choose  species  that  bloom  at 
different  seasons,  a  succession  of  flowers  may  be  had  from  the 
same  spot  during  the  summer.  In  mixed  plantings,  where  two 
kinds  of  flowers  are  to  bloom  at  once,  or  where  adjacent  plant- 
ings come  into  bloom  at  the  same  time,  one  must  avoid  the 
planting  together  of  inharmonious  colors,  such  as  magenta  and 
scarlet,  or  purple  and  blue.  White  flowers  may  be  used  to 
separate  warring  colors  and  also  to  serve  as  a  foil  for  all 
others.  Both  purple  and  blue  flowers  add  a  sense  of  distance 
to  the  view,  and,  if  planted  in  bays  in  the  shrubbery,  appear 
to  increase  the  size  of  the  garden.  Yellow  and  red  flowers 
have  the  opposite  effect.  By  planting  them  on  jutting  points 
they  add  to  the  apparent  depth  of  the  bays. 

Hedges.  In  some  cases  it  is  desirable  to  divide  two  plots  of 
ground,  or  to  set  off  the  home  grounds  from  the  street,  by  means 
of  a  hedge.  For  repelling  intruders  or  keeping  stock  within 
bounds,  the  hedge  is  made  of  some  thorny  material,  such  as 
Osage  orange,  honey  locust,  barberry,  or  buckthorn.  About 
dwellings  it  is  more  usual  to  plant  privet,  lilac,  box,  or  some 
of  the  evergreens  like  arbor  vitte  and  hemlock.  Hedge  plants 
are  set  thickly  in  straight  lines  and  are  trimmed  into  shape 
annually  during  the  summer  season.  The  words  "  hedge  "  and 
"  edge  "  are  obviously  of  similar  derivation,  and  edgings  are 
naturally  lines  of  small  plants  like  small  hedges  set  along  the 
borders  of  other  plantings.  Pansies,  alyssum,  lobelias,  and 
many  other  low-growing  species  are  used  for  this  purpose. 

Bulbs.  All  plants  propagated  by  thickened  underground 
parts  are  called  bulbs  by  the  florist  and  general  gardener, 
and,  for  the  purposes  of  planting,  no  other  distinction  need  be 
made.  The  chief  value  that  attaches  to  bulbs  is  found  m  the 
fact  that  the  flowers  are  usually  showy,  and,  being  formed  in 
the  preceding  summer,  are  practically  certain  to  appear  when 


208  AGRONOMY 

the  bulbs  are  properly  planted,  pushing  upward  almost  as  soon 
as  the  snow  is  gone  and  blooming  at  a  time  when  flowers  of 
any  kind  are  rare.  In  addition  to  the  spring  flowering  bulbs 
there  are  a  few  that  bloom  in  summer.  Summer  flowering 
species  are  nearly  always  tender  and  have  to  be  dug  up  and 
kept  from  the  cold  during  the  winter.  The  gladiolus  and 
tuberose  belong  to  this  class.  The  spring  flowering  bulbs  are 
not  only  hardy  but  they  have  to  be  planted  in  autumn  in  time 
to  make  root  growth  if  they  are  to  bloom  the  following  spring. 
During  summer  they  may  be  dug  up  and  stored  in  a  cool  dry 
place,  or  they  may  be  allowed  to  remam  in  the  soil  and  annuals 
planted  over  them.  Many  low-growing  species  may  be  natural- 
ized on  the  lawn  and  will  bloom  before  the  grass  is  high  enough 
to  require  cutting.  If  not  cut  too  closely  in  mowing,  they  will 
continue  to  bloom  from  year  to  year.  Taller  species,  such  as 
the  daffodil  and  narcissus,  are  occasionally  naturalized  along 
the  margin  of  streams  and  the  edges  of  woodlands,  where  they 
thrive  as  well  as  our  native  species.  In  planting  the  spring 
flowering  bulbs,  a  well-drained  spot,  protected  on  the  north  and 
west,  should  be  selected.  They  may  be  planted  in  masses  or 
formal  groups,  and  as  soon  as  the  ground  is  frozen  should  be 
covered  with  several  inches  of  coarse  straw,  leaves,  or  other 
litter.  In  spring  the  mulch  should  not  be  removed  until  the 
growing  plants  require  it ;  otherwise  they  may  be  injured  by 
the  cold.  In  the  public  parks  and  other  large  grounds  bulbs 
are  frequently  arranged  in  geometrical  and  other  designs. 

Carpet  bedding.  This  is  the  term  applied  to  a  form  of  plant- 
ing in  which  plants  with  bright-colored  foliage  are  arranged 
in  formal  designs  and  kept  trimmed  to  an  even  surface,  giving 
an  effect  not  unlike  a  carpet  or  rug.  Ribbon  bedding  is  much 
like  this,  since  it  consists  in  setting  plants  in  long,  straight 
rows.  This  kind  of  planting  may  be  used  along  walks  and  in 
other  situations  where  straight  lines  prevail,  but  is  not  adapted 
to  plantings  in  the  natural  style. 


DECOEATIVE  PLANTING 


209 


Formal  planting.  The  rules  for  planting  given  in  this  book 
are  for  that  style  of  gardening  known  as  the  English  or  natural 
style.  It  is  patterned  closely  after  nature  and  is  the  one  most 
in  use  in  the  United  States  and  Great  Britain.  A  more  formal 
method,  known  as  the  Italian  ov  geometrical  style,  once  in  great 
vogue  and  still  extensively  used  in  parks  and  large  estates, 
consists  in  making  all  planting  on  geometrical  lines.  Here 
clipped  shrubs,  plants  in  vases,  sundials,  pergolas,  angular 
beds,  balustrades,  terraces,  arbors,  fountains,  statuary,  weeping 
trees,  carpet  bedding,  and  straight  lines  find  an  appropriate 


Photograph  from  Wagner  Park  CoiiBervatories,  Sidney,  Ohio 

Fig.  154.   A  formal  garden 
Note  how  this  planting  harmonizes  with  the  style  of  architecture 

use,  and  when  thus  assembled  have  an  attractiveness  that  is 
beyond  question.  Such  planting,  however,  is  out  of  place  in 
the  small  lawn  unless  the  entire  area  is  treated  in  the 
same    style. 

Transplanting  shrubs  and  trees.  As  a  rule,  shrubs  and 
trees  cannot  be  transplanted  with  safety  when  in  full  leaf. 
They  are  usually  moved  in  autumn  after  the  leaves  have  fallen 
or  in  spring  before  the  buds  have  pushed  forth,  but  if  care  is 
taken  to  keep  the  plants  from  drying  out,  they  may  be  moved 
in  spring  until  the  leaves  are  nearly  full  grown.  Nurserymen 
commonly  prolong  the  planting  season  by  digging  up  their 
stock  in  autumn  and  keeping  it  in  cold  storage  until  wanted. 


210 


AGRONOMY 


Specimens  may  thus  be  had  in  a  dormant  condition  long  after 
the  same  kinds  of  plants  in  the  field  have  produced  their 
leaves.  In  transplanting  trees  and  shrubs  tlie  rules  that  govern 
the  transplanting  of  garden  plants  in  general  may  be  observed. 
If  many  of  the  large  roots  have  been  severed  in  digging,  the 
top  of  the  specimen  must  be  cut  back  to  balance  the  loss  and 


Photograph  t)y  Wagner  Park  Consenatories,  Sidney,  Ohio 


¥iQ.  155.   The  natural  style  of  planting  applied  to  the  home  grounds 


prevent  too  great  transpiration.  In  doing  this  it  is  better  to 
remove  weak  branches  and  superfluous  twigs  rather  than  to 
cut  off  the  top  or  main  branches  and  thus  destroy  the  natural 
shape  of  the  specimen.  In  the  case  of  shrubs,  when  it  may 
be  desirable  to  retain  as  many  branches  as  possible,  the  leaves 
only  may  be  removed.  The  removal  of  the  leaves  is  also  prac- 
ticed in  moving  shrubs  in  early  autumn  before  the  leaves 
have  fallen.    The  roots  should  never  be  allowed  to  become 


DECORATIVE  PLAITTING  211 

dry  while  transplanting,  and,  before  the  specimen  is  set,  all 
broken  and  bruised  roots  should  be  cut  back  to  the  sound 
wood  with  a  sharp  clean  cut.  Specimens  should  be  set  slightly 
deeper  than  they  stood  originally,  and  it  is  well  to  have  the 
same  side  toward  the  north.  The  hole  in  which  the  plant  is 
to  be  set  should  always  be  large  enough  to  allow  the  roots  to 
spread  out  naturally.  This  hole  is  sometimes  made  by  explod- 
ing a  small  charge  of  dynamite,  which  loosens  the  subsoil  and 
makes  it  easy  for  the  new  roots  to  penetrate  it.  The  best  soil 
should  be  used  for  filling  about  the  roots  and  should  be  well 
firmed  about  them.  If  the  plant  is  set  in  poor  soil,  enough 
good  soil  should  be  procured  elsewhere  to  fill  up  the  hole. 
When  the  hole  is  half  filled,  the  plant  may  be  gently  worked 
up  and  down  to  settle  the  earth  about  the  roots,  or  water 
may  be  thrown  into  the  hole  for  the  same  purpose.  No  air 
spaces  about  the  roots  should  be  permitted. 

Transplanting  herbaceous  perennials.  As  with  the  woody 
plants,  the  best  time  to  transplant  herbaceous  perennials  is  in 
fall  or  spring,  but  owing  to  the  fact  that  these  plants  are 
smaller  and  more  easily  handled,  they  may  be  moved  at  any 
time  if  a  few  simple  rules  are  observed.  In  the  case  of  wild 
plants,  many  of  which  are  among  our  most  ornamental  spe- 
cies, the  rule  most  frequently  followed  is,  "  Transplant  when 
you  find  them."  By  using  care  in  the  digging,  keeping  the 
specimen  moist,  and  protecting  from  the  sun  until  established 
in  the  new  locality,  one  can  move  almost  any  specimen  without 
loss  even  when  in  bloom. 

Mulching  and  heeling  in.  Newly  set  herbaceous  plants  are 
benefited  by  a  light  mulch  over  their  roots,  which  keeps  the 
moisture  from  evaporating  and  the  soil  from  baking.  Plants 
set  in  autumn  should  be  more  heavily  mulched  as  soon  as  the 
ground  is  frozen,  and  this  should  not  be  removed  until  the 
frost  is  out  of  the  ground  in  spring.  Such  a  mulch  prevents 
the  heaving  due  to  the  alternate  thawing  and  freezing  of  the 


212  AGRONOMY 

ground,  and  is  especially  desirable  in  the  case  of  plants  in 
exposed  places.  More  plants  are  killed  annually  by  having 
their  roots  broken  when  heaved  by  the  frost  than  by  the  cold 
of  winter  itself.  It  often  happens  that  more  plants  are  dug 
than  can  properly  be  planted  at  one  time,  and  in  such  cases 
the  surplus  is  heeled  in  until  they  can  be  planted.  In  heeling 
in,  a  trench  is  dug  deep  enough  to  receive  the  roots,  and  the 
plants  are  placed  within  this  in  such  a  way  that  the  tops  rest 
on  the  earth.  Soil  is  then  thrown  on  the  roots  in  widening 
the  trench,  and  then  another  layer  of  plants  with  tops  over- 
lapping the  first  is  put  in,  and  so  on.  Plants  are  frequently 
heeled  in  over  winter.  In  such  cases  the  roots  should  be 
heavily  mulched  as  soon  as  the  ground  is  frozen,  but  if  the 
tops  are  mulched,  it  may  form  a  retreat  for  mice  that  may 
damage  the  bark  or  buds.  Plants  should  always  be  heeled  in 
in  a  light,  well-drained  spot. 

Treatment  of  woodlands.  The  ever-increasingr  demand  for 
wood  in  various  industries  has  greatly  dimmished  the  immense 
forests  that  once  covered  our  country,  and  the  remnant  is  fast 
disappearing.  All  this  greatly  enhances  the  value  of  the  tim- 
ber still  standing.  In  some  regions  trees  are  already  treated 
as  farm  crops,  and  everywhere  there  is  being  manifested  a 
desire  to  manage  the  woodlands  so  that  the  greatest  amount 
of  timber  may  be  obtained  from  the  area  they  cover.  Formerly 
it  was  the  custom  to  cut  down  the  entire  stand  of  trees  in 
lumbering  and  to  clear  the  ground,  but  at  present  in  all 
forests  where  conservative  methods  are  practiced,  only  the 
marketable  timber  is  removed  and  the  remamder  is  left  to 
produce  a  new  crop.  The  forests  may  thus  be  made  to  yield 
perennial  supplies.  Properly  cared  for,  most  forests  will  con- 
tinue to  reproduce  themselves.  When  this  does  not  occur  nat- 
urally, it  is  usual  to  plant  young  trees  of  the  desired  variety. 
In  all  broken  country  there  are  many  areas  too  steep  or  too 
infertile  to  produce  ordmary  crops,  but  on  which  excellent 


DECORATIVE  PLANTING  213 

timber  can  be  grown.  Many  of  these  are  being  reforested  by 
planting  with  young  trees.  It  is  probable  that  in  time  all 
such  regions  will  be  again  covered  with  forest.  At  present  a 
wood  lot  managed  as  a  growing  crop  of  fence  posts,  railway 
ties,  and  telegraph  poles  may  be  made  to  yield  quite  as  much 
as  the  same  area  planted  to  annual  crops,  and  with  no  greater 
amount  of  labor  or  capital  spent  upon  it.  The  steadily  advanc- 
ing prices  of  all  kinds  of  timber  make  it  clear  that  in  future 
a  much  greater  revenue  may  be  derived  from  such  wood  lots 
than  from  the  ordinary  crops. 

Enemies  of  the  forest.  The  three  greatest  dangers  that 
threaten  the  forest,  aside  from  wasteful  cutting,  are  fires,  in- 
sects, and  plant  diseases.  To  reduce  these  to  a  minimum,  it 
is  desirable  that  all  dead  and  dying  trees  and  underbrush  that 
might  furnish  food  for  the  fire  or  a  lurking  place  for  insects 
and  fungi  be  removed.  Vigorous  trees  are  least  susceptible 
to  insect  and  fungous  attacks,  and  only  the  best  trees  should 
be  left  to  grow.  The  misshapen  specimens  and  others  that 
crowd  the  good  trees  for  light  and  room  should  be  removed. 
In  the  forest,  trees  whose  timber  is  of  no  value  are  as  much 
weeds  as  are  mustard  and  pigweed  in  a  field  of  grain.  In 
extensive  forests,  where  injury  from  fires  is  most  likely  to 
occur,  the  ground  is  divided  into  sections  by  fire  lanes  — 
broad,  cleared  strips  wide  enough  to  confine  the  forest  fire, 
once  started,  to  a  single  section.  The  custom  of  allowing 
cattle  to  graze  in  the  forest  is  extremely  harmful,  since  the 
young  trees  are  destroyed  and  the  perpetuation  of  the  forest 
prevented. 

Quite  aside  from  their  value  as  a  source  of  timber  and  fuel, 
forests  are  of  great  benefit  in  preventmg  floods  by  delaying 
the  run-off  from  rain  and  melting  snow.  In  forested  areas 
much  of  this  moisture  sinks  into  the  soil,  to  reappear  later  in 
springs  which  keep  the  small  streams  from  drying  up  in 
summer. 


214  AGRONOMY 

PRACTICAL  EXERCISES 

1.  Make  a  planting  plan  for  a  city  lot  of  average  size  on  a  scale  of 
^  or  -^  in.  to  the  foot,  indicating  on  it  the  house,  walks,  and  drives,  and 
the  location  and  nature  of  the  planting. 

2.  From  a  catalogue  of  decorative  plants,  to  be  had  of  any  nursery- 
man for  the  asking,  select  and  list  the  species  suggested  for  planting 
your  plan. 

3.  With  such  suggestions  as  seem  desirable  for  improving  the  plant- 
ing, make  a  similar  plan  of  your  home  grounds  or  of  the  school  grounds. 

4.  Visit  parks,  cemeteries,  and  private  grounds  for  studies  in  good 
and  bad  planting  effects. 

5.  If  there  are  Italian,  or  formal,  and  Japanese  gardens  within 
reach,  visit  them  and  compare  with  the  natural  style  of  planting. 

6.  Make  a  planting  plan,  drawn  to  scale,  of  some  small  park  in 
the  vicinity,  or  make  a  planting  plan  for  turning  some  near-by  vacant 
space  into  a  park. 

7.  Select  desirable  plants  and  plant  a  section  of  the  school-garden 
border. 

8.  On  Arbor  Day  plant  one  or  more  trees  or  shrubs  on  the  school 
grounds,  in  the  school  garden,  or  in  your  home  grounds. 

9.  At  the  beginning  of  winter  nuilch  all  plants  in  the  school  garden 
that  are  likely  to  be  harmed  by  the  cold.  Do  the  same  for  your  own 
grounds. 

10.  Make  one  or  more  trips  to  a  public  park  or  large  private  estate, 
and  list  all  the  shrubs  found  in  bloom.  Make  a  similar  list  of  all  the 
perennials. 

11.  By  the  use  of  a  good  botanical  manual  name  all  the  shrubs  and 
perennials  as  they  bloom  in  the  school  garden  and  near-by  fields  during 
the  time  devoted  to  this  course. 

12.  Remove  to  the  school-garden  borders  for  observation  all  abnor- 
mal iilants  encountered,  such  as  four-leaved  clovers,  albinos,  fasciated 
stems,  and  the  like. 

References 

Bailey,  "Manual  of  Gardening." 
Maynard,  "Landscape  Gardening." 
Parsons,  "Landscape  Gardening  Studies." 
Waugh,  "The  Landscape  Beautiful." 
Waugh,  "  Landscape  Gardening." 


CHAPTER  XV 


PRUNING 


Purpose  of  pruning.  The  object  of  pruning  is  to  repair  inju- 
ries, promote  the  proper  growth  of  the  specimens,  and  secure 
more  shapely,  liealtliy,  and  fruitful  plants.  Many  species  grow 
so  luxuriantly  that 
they  require  an  an- 
nual trimming  to 
keep  them  within 
bounds.  Others, 
again,  may  produce 
a  crown  of  foliage 
so  dense  that  suffi- 
cient light  and  air 
do  not  penetrate 
it;  in  consequence 
of  this  few  flower 
buds  are  formed, 
and  what  fruit  is 
produced  is  pale  in 
color  and  poorly 
flavored.  Such  a 
specimen  is  ben- 
efited by  pruning. 
Although  woody 
species  are  the  ones  usually  pruned,  a  few  herbaceous  plants 
commonly  receive  the  same  treatment,  especially  tomatoes, 
tobacco,  okra,  and  various  garden  flowers.  Many  woody 
plants  are  self-pruning  and  annually  cut  off  many  of  their 

215 


Photograph  by  II.  L.  IIoIliBter  Land  Co. 

Fig.  156.    Apple  blossoms 
Showing  the  good  results  of  proper  pruning 


216 


AGRONOMY 


young  twigs.  The  habit  of  cutting  off  the  useless  flowers  after 
blooming  may  also  be  regarded  as  a  form  of  self-pruning,  as  is 
the  casting  of  the  leaves  in  autumn.  It  is  commonly  supposed 
that  only  flowers  that  fail  to  be  pollinated  are  cut  off  by  the 
plant,  but  many  young  fruits  are  also  severed  from  the  branches, 
otherwise  the  plant  could  not  make  sufficient  food  for  all,  and 
even  if  it  could,  the  load  would  be  more 
than  it  could  bear.  The  advantages  to 
be  derived  from  thinning  the  fruit  on 
trees  heavily  loaded  is  obvious. 

Time  to  prune.  An  old  rule  for 
pruning  is,  "  Prune  when  the  knife  is 
sharp,"  indicating  that  when  a  plant 
needs  pruning  one  time  is  as  good  as 
another,  but  such  a  rule  has  many  ex- 
ceptions. The  time  for  pruning  any 
plant  depends  somewhat  upon  the  time 
at  which  it  produces  its  flowers.  Plants 
that  form  their  flower  buds  in  autumn 
should  not  be  pruned  in  winter,  as  this 
would  remove  the  embryo  flowers  and 
fruits.  Such  plants  should  be  pruned 
in  spring  and  summer,  shortly  after 
they  have  fruited  and  before  new  flower 
buds  have  been  formed.  On  the  other 
hand,  many  plants  produce  their  flowers 
on  the  new  wood,  that  is,  on  twigs  produced  from  winter  buds. 
These  may  be  pruned  in  winter,  since  new  and  vigorous  wood 
will  usually  be  more  floriferous  than  older  twigs.  In  general, 
winter  pruning  increases  the  amount  of  wood  formed  and  sum- 
mer pruning  induces  flowering.  Summer  pruning  has  the  ad- 
vantage over  winter  pruning  in  that  one  may  then  see  how 
the  crown  of  foliage  .is  displayed  and  may  more  readily 
remove  branches  that  shade  others.    Moreover,  the  cambium, 


Fig.  157.  A  common  form 
'     of  pruning  shears 


PRUNING 


21T 


active  at  this  season,  soon  covers  the  wound  with  a  protective 
layer  of  bark.  One  should  be  careful  not  to  overprune  ;  a  little 
pruning  yearly  is  much  better  than  more  at  longer  intervals. 

Pruning  implements.  A  good  sharp  knife  is  a  most  efficient 
pruning  instrument,  and  the  intelligent  horticulturist  seldom 
needs  anything  else.  Prun- 
ing shears  with  stout  blades 
may  take  the  place  of  the 
knife,  but  when  shrubbery 
has  been  allowed  to  go  for 
some  time,  large  branches 
may  require  the  use  of 
a  saw.  There  are  various 
kinds  of  pruning  shears 
and  saws  on  the  market, 
some  forms  of  the  latter 
having  teeth  on  both  sides 
of  the  blade. 

Methods  of  pruning. 
There  are  several  rules 
that  may  be  observed  in 
pruning  any  shrub  or  tree. 
It  is  always  proper  to  re- 
move branches  that  shade 
others  as  well  as  those  that 
grow  toward  the  interior 
of  the  crown.  These  latter 
are  soon  ciit  off  from  the 
light  by  the  growth  of  tlie 
outside  branches,  and,  if  not  removed,  would  soon  die  anyway. 
Branches  that  have  grown  too  rapidly  for  the  symmetry  of 
the  plant  may  be  cut  back,  but  in  all  cases  where  part  of  a 
twig  is  removed  care  must  be  taken  to  cut  above  a  bud  facing 
outward,  else  the  new  growth  is  likely  to  grow  toward  the 


Fig.  158.    An  apple  tree 

An  example  of  improper  pruninjj;.  The  tree 

lias  been  allowed  to  grow  so  liigli  that  it  is 

difficult  to  gather  the  fruit 


218  AGRONOMY 

center.  In  selecting  the  branches  to  remain,  every  endeavor 
should  be  made  to  have  no  gaps  in  the  crown  of  foliage.  There 
should  be  enough  branches  to  fill  it  out  on  all  sides.  In  shap- 
ing young  fruit  trees  and  the  like,  the  branches  should  not  be 
allowed  to  spring  from  a  common  point,  and  all  forks  should 
be  avoided.  Looking  down  upon  the  specimen  and  imagining 
a  circle  with  the  trunk  of  the  plant  in  the  center,  endeavor  to 
train  it  in  such  a  way  that  from  three  to  five  main  branches 
radiate  out  at  equal  distances  and  form  the  framework  of  a 
well-balanced  crown.  In  setting  young  fruit  trees  they  are 
sometimes  pruned  to  mere  whips  and  a  new  head  developed 
from  the  fresh  twigs  that  will  spring  forth.  Orchard  trees  are 
usually  heeided  low  to  facilitate  gathering  the  fruit. 

Making  the  cut.  In  removing  branches  all  cuts  should  be 
made  close  to  the  stem,  and  no  stubs  left  to  harbor  insects  and 
the  germs  of  disease.  In  removing  very  large  limbs  there  is 
always  danger  that  they  may  fall  by  their  own  weight  and 
thus  tear  down  the  bark  and  wood  of  the  main  stem  before  the 
cut  is  complete.  This  may  be  avoided  by  first  making  a  cut 
part  way  through  the  branch  on  the  underside  and  a  foot  or 
more  from  the  trunk.'  A  cut  from  above  meeting  this  or  a 
little  beyond  it  will  sever  the  limb,  after  which  the  stub  may  be 
sawed  off  close  to  the  trunk.  If  the  branch  removed  is  more 
than  an  inch  in  diameter,  the  wound  should  be  immediately 
covered  with  a  coat  of  paint  or  grafting  wax  to  keep  out  injury 
from  the  weather,  bacteria,  and  insects.  Scars  left  by  the 
removal  of  smaller  branches  may  be  disregarded,  as  the  tree 
will  soon  cover  them  with  bark. 

Specimens  needing  little  pruning.  The  evergreen  trees  should 
never  be  pruned.  When  properly  grown  the  branches  radiate 
on  all  sides  from  the  ground  up,  and  the  trees  lose  much  of 
their  beauty  when  trimmed  like  other  trees.  An  evergreen 
tree,  once  deprived  of  its  lower  branches,  rarely  renews  them. 
Shade  trees  seldom  require  pruning  except  to  remove  dead 


PEUNING 


219 


branches  and  to  repair  damage  by  storm.  Many  shrubs  also, 
among  which  are  Ulacs,  deutzias,  spiraeas,  and  forsythias,  do 
well  without  much  pruning.  The  plants  most  frequently 
pruned  are  those  grown  for  their  fruit,  and  the  object  in 
pruning  is  to  force  them  to  bear  more  and  better  crops  by  the 
production  of  new  wood  upon  which  the  fruits  are  borne.    In 


Photograph  by  11.  L.  Hollister  Land  Co. 

Fig.  159.    Cherry  trees  in  bloom  in  an  irrigated  orchard 

temperate  regions  flowers  seldom  appear  on  wood  that  is  more 
than  two  years  old.  In  the  tropics  flowers  often  appear  on  the 
large  branches  or  even  the  trunks  of  trees.  In  the  hands  of  the 
skilled  gardener  all  the  flowering  shrubs  may  be  induced  to 
bear  the  maximum  number  of  flowers  by  judicious  pruning. 

Pruning  special  crops.  Some  plants  produce  but  one  crop 
of  flowers  and  fruits  on  a  branch,  no  matter  how  long  it  may 
remain  on  the  plant  after  fruiting,  and  such  branches  are  as 


220 


AGRONOMY 


well  removed  as  not.  Other  species  form  certain  short  branches, 
called  fruit  spurs,  that  bear  many  successive  crops.  It  is  neces- 
sary, therefore,  to  know  how  each  specimen  fruits  before  it  can 
be  pruned  intelligently.  The  raspberry 
and  hlaekherry  always  fruit  on  canes 
grown  the  previous  year  and  do  not 
bear  fruit  on  these  canes  a  second  time. 
As  soon,  therefore,  as  the  fruiting  season 
is  over,  the  old  canes  should  be  removed 
to  make  room  for  the  new  ones.  When 
the  latter  have  reached  a  height  of  two 
or  three  feet,  the  tips  are  also  removed, 
which  causes  side  branches  to  form  and 
increases  the  wood  upon  which  the  fruit 
is  borne.  In  grapes  the  fruit  is  borne 
upon  the  new  wood,  that  is,  upon  wood 
produced  the  same  year  as  the  fruit.  In 
training  these  plants  it  is  customary  to 
allow  one  or  more  main  stems  to  grow, 
and  these  are  trained  upon  posts,  wires, 
or  trellises.  From  each  joint  of  these 
stems  a  branch  arises  which  bears  fruit. 
After  the  crop  is  gathered  these  young 
branches  are  cut  back  nearly  to  the 
main  stem,  only  mere  stubs  with  two 
or  three  buds  being  left.  The  following 
season,  when  these  buds  begin  to  grow, 
the  best  are  selected  to  form  the  fruiting 
branches  for  that  year.  Grapes  should 
be  pruned  when  perfectly  dormant.  If 
pruned  later  than  February,  they  are  likely  to  bleed  and  to  be 
harmed  thereby.  Apples,  pears,  and  cherries  form  short  fruit 
spurs  on  the  old  wood.  These  bear  fruit  year  after  year,  and 
care  should  be  taken  not  to  injure  them  when  pruning  or 


Fig.  100.   Fruit  spurs  on 

the  second-year  wood  of 

cherry  which  may  bear 

several  crops 


PRUNING 


221 


when  gathering  the  fruit.  Short- 
ening the  new  growth  of  these 
trees  induces  the  formation  of 
more  fruit  spurs.  The  peach  fruits 
on  wood  one  year  old ;  that  is, 
branches  produced  one  summer 
should  fruit  the  next.  Since  check- 
ing the  growth  favors  fruiting,  cut- 
ting back  part  of  the  new  growth 
late  in  summer  influences  the 
formation  of  flower  buds.  The 
peach  is  a  luxuriant  and  rapid 
grower,  and,  if  allowed  to  go 
unpruned,  is  likely  to  produce 
more  wood  than  fruit.  Currants 
produce  fruit  on  both  the  old 
and  new  wood,  but  wood  more 
than  three  years  old  is  considered 
unprofitable  and  may  be  removed. 
The  new  growth  tends  to  produce 
more  fruit  buds  if  it  is  pinched 
back  to  leave  from  two  to  six 
buds  on  each  twig. 

Thinning.  Thinning,  or  the  re- 
moval of  some  of  the  fruit  when 
the  tree  is  overloaded,  is  a  form 
of  pruning.  Several  advantages 
are  gained  by  thinning.  If  all  the 
fruit  is  left  on  the  tree,  the  load 
may  be  so  great  as  to  break  the 
branches,  while  the  effort  to  pro- 
duce so  great  a  crop  results  in  a 
quantity  of  undersized,  flavorless 
specimens.   It  is  much  better  to 


Fig.  IGl.    Two-year-old  twig  of 
the   peach   showing  three  pedi- 
cels,   or   stalks,   that    produced 
fruit  and  will  not  bear  again 


Photo^'raph  by  U.  L.  HoUister  Land  Co. 

Fig.  162.   Peaches  growing  on  wood  of  the  preceding  year 


PhotoL'raph  by  H.  L.  IIoHister  Land  Co. 

Fig.  103.    An  overloaded  branch  of  a  plum  tree 

The  fruit  should  be  thinned  by  removing  all  .small  or  imperfect  specimens 

222 


PRUNING  223 

remove  some  of  the  fruit  than  to  endeavor  to  save  it  all  by 
propping  up  the  limbs.  Overbearing  may  also  weaken  the 
plant  so  much  as  to  prevent  all  fruit  bearing  the  following 
season.    In  thinning,  the  effort  should  be  made  to  have  the 


I'liulograpL  by  II.  L.  IloUiuter  Laud  Co. 

Fig.  164.   Rome  Beauty  apples 
Note  that  the  fruit  is  produced  from  short  spurs  on  the  old  wood 

fruit  uniformly  scattered  over  the  tree.  The  inferior  and 
poorly  placed  specimens  are  of  course  the  ones  to  be  removed. 
Wormy  and  defective  fruits  may  often  be  brought  down  by 
gently  shaking  the  tree  occasionally. 


224 


AGRONOMY 


Heading  in.  ]\Iany  species,  especially  when  young,  make 
such  luxuriant  growth  that  some  of  it  needs  to  be  removed  in 
order  that  the  rest  may  ripen  into  strong  wood.    Removal  of 


Photograph  by  H.  L.  IlolUster  Land  Co. 

Fig.  165.   A  heavily  loaded  branch  of  currants 

the  excess  growth  is  called  heading  in.  The  peach,  pear,  crab, 
and  poplar  are  among  those  most  frequently  headed  in,  but 
any  rank-growing  species  may  need  it.    When  nearly  all  the 


PRUNING 


225 


crown  is  removed,  by  cutting  off  the  main  branches,  this  is 
called  pollarding.  Poplars  and  willows  are  often  pollarded,  but 
other  trees  may  be  ruined  by  this  process.    Heading  in  may 


Photograph  by  II.  L.  Uollieter  Land  Co. 

Fig.  166.  Young  plum  tree,  heavily  loaded  with  fruit,  grown  under  irrigation 

be  rendered  unnecessary  by  removing  the  tips  of  the  tender 
growth  with  the  thumb  and  finger  when  it  has  reached  the 
desired  length.    This  latter  operation  is  called  pinching  or 


226  AGRONOMY 

stopping.  In  annual  plants  pinching  induces  both  branching 
and  flowering.  Melon  and  cucumber  vines  are  often  stopped  to 
make  them  fruit  earlier,  and  raspberries  and  blackberries  are 
regularly  pinched  to  cause  branching.  Since  the  majority  of 
buds  form  twigs,  the  removal  of  the  buds  may  take  the  place 
of  pruning.  This  is  called  disbudding.  In  annual  plants  dis- 
budding is  often  used  to  throw  the  strength  of  the  plant  into 
a  few  superior  flowers  or  fruits.  The  florist  regularly  increases 
the  size  of  chrysanthemum  flowers  by  removing  all  but  the 
terminal  buds.  Other  forms  of  pinching  that  are  self-explana- 
tory are  topping,  detasseling,  and  suckering. 

Root  pruning.  In  rich  soils  trees  sometimes  fail  to  fruit  be- 
cause of  too  exuberant  growth.  In  such  cases  fruiting  may 
be  induced  by  anything  that  will  check  the  vegetative  func- 
tions. This  is  often  exemplified  in  trees  that  have  been  injured 
by  lightning,  defoliated  by  insects,  subjected  to  an  extended 
drought,  or  planted  in  sterile  soil.  Under  any  of  these  condi- 
tions they  are  likely  to  begin  fruiting.  A  geranium  plant 
blooms  most  freely  when  it  has  become  pot-bound,  that  is, 
when  the  soil  in  the  pot  is  crowded  with  roots,  and  removing 
part  of  the  root  system  of  a  plant  has  the  same  effect.  All 
fruiting  may  be  regarded  as  a  life-saving  process,  in  that  it 
provides  the  plant  with  a  means  for  continuing  the  species, 
and  any  injury  is  likely,  therefore,  to  call  it  into  action.  One 
of  the  most  frequent  methods  in  use  is  root  pruning,  in  which 
a  trench  is  dug  around  the  tree  and  some  of  the  feeding  roots 
cut  off,  or  a  sharp  spade  may  be  driven  into  the  soil  at  the 
proper  distance  for  this  purpose.  The  roots  usually  extend  as 
far  out  as  the  branches ;  therefore  the  distance  from  the  tree 
at  which  the  roots  should  be  severed  depends  upon  its  size. 
Care  should  be  taken  not  to  remove  too  many  roots  at  one 
time,  else  the  plant  may  be  injured.  The  purpose  is  merely  to 
check  the  growth.  In  some  cases  it  is  best  to  remove  part  of 
the  roots  one  year  and  more  the  next. 


PRUNING 


227 


Girdling.  Removing  a  zone  of  bark  from  a  tree  will  kill  it 
because  the  plant  food  which  passes  down  through  the  bark  to 
the  roots  can  no  longer  reach  them  and  they  die  of  starvation. 
Girdling  a  fruiting  branch,  however,  may  increase  the  size  of 
the  fruit  it  bears  by  retaining  in  it  all  the  plant  food  made  by 
the  leaves.  At  the  end  of  the  season  the  branch,  of  course, 
dies,  since  the  removal  of  the  bark  kills  the  cambium  and  pre- 
vents the  formation  of  new  ducts.    In  plants  like  the  grape. 


Photograph  by  II.  L.  Ilollistcr  Land  Co. 

Fig.  167.    Young  apple  orchard  in  the  Northwest 

The  darker  speoimens  are  peach  trees  which  will  yield  several  crops  of  fruit 
hefore  they  have  to  he  removed  to  make  room  for  the  apple  trees 


where  the  fruiting  branch  is  removed  at  the  end  of  the  season 
anyway,  this  method  is  occasionally  employed.  When  a  valu- 
able tree  is  girdled,  it  may  sometimes  be  saved  by  at  once  re- 
ducing the  top  to  lessen  evaporation,  and  protecting  the  wound 
until  new  bark  can  form  over  it.  Bridge  grafting  may  also  be 
resorted  to  in  helping  the  tree  to  cover  the  wound. 

Cavities  and  broken  limbs.    When  decay  has  been  allowed 
to  go  unchecked  until  a  cavity  has  been  formed  in  the  trunk 


228  AGRONOMY 

of  a  tree,  the  life  of  the  specimen  may  be  prolonged  by  filling 
the  cavity  with  cement.  Before  puttuig  in  the  cement  all  the 
dead  wood  should  be  removed  and  the  cavity  sterilized  with 
any  good  disinfectant  such  as  corrosive  sublimate  or  copper 
sulphate.  It  is  also  well  to  give  the  cavity  a  good  coat  of  paint 
or  tar.  If  it  is  very  large,  concrete  may  be  used  as  a  filling 
and  cement  used  to  finish  off  the  work.  The  edges  of  the 
cavity  should  be  straightened  up  and  painted,  and  under 
normal  conditions,  if  the  cement  has  been  made  just  even  with 
the  wood,  the  bark  should  soon  grow  over  the  wound.  When 
a  limb  has  been  partly  split  off  from  a  tree,  or  when  the  trunk 
has  been  split  by  a  storm,  it  may  often  be  saved  by  bolting  it 
together  by  an  iron  bolt  extending  through  both  parts.  Bind- 
ing the  two  together  with  wire  serves  only  to  increase  the  in- 
jury, since  this  soon  stops  the  movement  of  sap  and  causes 
death  to  the  parts. 

Topiary  work.  That  form  of  ornamental  gardening  in  which 
trees  and  shrubs  are  sheared  into  grotesque  forms,  often  sim- 
ulating animals  and  the  like,  is  called  topiary  work.  For  this 
purpose  evergreen  species  are  usually  employed.  Hedges,  ar- 
bors, and  arches  are  forms  of  topiary  work.  Other  examples 
may  often  be  seen  in  old  cemeteries  and  on  large  private 
grounds.  In  the  formal  style  of  gardening  the  less  grotesque 
forms  are  allowable,  but  all  are  out  of  place  on  home  grounds. 

PRACTICAL  EXERCISES 

1.  Visit  parks,  private  grounds,  and  the  trees  along  the  streets  for 
examples  of  pruning.  Do  you  find  any  trees  that  need  pruning?  any 
that  have  been  badly  pruned  V  Make  suggestions  for  improvement. 

2.  If  there  are  no  trees  in  the  school  garden  to  be  i)runed,  visit  a 
bushy  field  or  neglected  roadside  and  practice  upon  the  shrubs  and  trees 
found  there. 

3.  Examine  fruiting  apple,  peach,  and  plum  trees,  raspberry  and  cur- 
rant bushes,  and  grapevines  to  discover  where  the  fruit  is  borne.  Later  in 
the  season  identify  the  flower  buds  on  species  that  form  them  in  autumn. 


PRUNING  229 

4.  If  there  are  any  trees  iu  the  neighborhood  that  have  been  pol- 
larded, visit  them  for  study. 

5.  Try  the  eifect  of  girdling  the  branch  of  some  tree  that  can  be 
spared. 

6.  Pinch  back  melons,  cucumbers,  cosmos,  and  various  erect-growing 
plants  and  compare  the  subsequent  growth  with  that  of  others  of  the 
same  kind  that  have  not  been  so  treated. 

7.  Visit  cemeteries,  parks,  and  large  private  grounds  for  examples 
of  topiary  work. 

8.  Remove  all  but  the  principal  flower  bud  from  a  plant  and  com- 
pare the  size  of  the  single  flower  thus  produced  with  that  of  the  flowers 
on  a  similar  plant  that  has  not  been  disbudded. 

9.  If  there  are  hedges  on  the  school  grounds,  prune  them ;  if  not, 
select  a  desirable  spot  and  plant  one. 

10.  Select  two  tomato  jilants  as  nearly  alike  as  possible.  Remove 
all  suckers  from  one  as  soon  as  they  appear  and  allow  the  other  to  grow 
naturally.  How  does  the  fruit  of  the  two  plants  compare  in  size  ?  in 
number  ?   in  total  weight  ? 

11.  Repair  any  cavities  in  the  trees  on  the  school  grounds  by  the 
method  described  in  this  book. 

References 

Bailey,  "The  Pruning  Book," 
Bailey,  "  Manual  of  Gardenhig." 
Fernow,  "The  Care  of  Trees." 

Farmer^  Bulletin 

181.  Pruning. 


CHAPTER  XVI 

PLANT  DISEASES 

Origin.  Plants,  like  animals,  are  afflicted  with  diseases  which 
are  caused  for  the  most  part  by  low  forms  of  plant  life  belong- 
ing to  the  great  group  known  as  the  Thallophytes.  Most  of 
these  are  bacteria  or  fungi  —  plants  without  chlorophyll  and 
therefore  reduced  to  the  necessity  of  gettmg  their  food  ready- 
made  from  other  organisms.  In  nourishing  themselves  they 
tear  down  the  tissues  of  the  specimen  upon  which  they  liave 
fastened,  and  in  due  time,  if  unchecked,  may  cause  its  death. 
Not  all,  however,  thrive  upon  living  things.  There  are  vast 
numbers  that  find  sustenance  in  the  bodies  of  dead  animals 
and  plants  and  even  in  their  cast-off  parts.  Of  the  latter 
type  are  the  bacteria  of  the  soil  that  turn  dead  vegetation  into 
nitrates  and  the  organisms  of  decay  that  resolve  dead  bodies 
back  into  the  elements  from  which  they  came,  thus  relieving 
the  soil  of  forms  that  would  otherwise  encumber  it.  We  can 
easily  imagine  the  confusion  that  would  exist  if  all  the  leaves 
that  have  fallen  in  the  forest  had  remained  as  they  were  when 
they  fell.  The  majority  of  the  fungi  and  bacteria  must  be 
classed  as  helpful  species ;  it  is  only  when  they  attack  the 
things  we  value  that  they  become  enemies.  As  regards  the* 
manner  in  which  they  feed,  plant  pests  may  be  divided  mto 
parasites  and  saprophytes.  Parasites  feed  upon  living  thmgs, 
and  saprophytes  upon  dead  ones.  The  organism  preyed  upon 
is  called  the  host.  In  general,  parasites  are  much  smaller  than 
saprophytes.  The  parasites  are  again  divided  into  the  external 
parasites,  which  live  upon  the  exterior  of  the  plant  and  send 
special   organs    into  its    tissues  for   food ;  and   the    internal 

230 


PLANT  DISEASES 


231 


parasites,  which,  safe  within  the  tissues  of  their  hosts,  bid 
defiance  to  most  attempts  to  dislodge  or  kill  them.  All  the 
fungi  spread  by  means  of  spores,  minute  one-celled  bodies  that 
function  like  the  seeds  of  flowering  plants.    They  are  often 


Fig.  168.    Live  oak  in  Audubon  Park,  New  Orleans,  covered  witli  Spanish 

moss  {Tillandsia) 

This  is  often  regarded  as  a  parasite,  but  it  is  an  independent  plant 

given  off  in  inconceivable  numbers.  The  common  field  mush- 
room produces  two  thousand  million  spores.  Others  are  capa- 
ble of  shedding  a  million  spores  a  minute  and  keeping  this  up 
for  several  days.  The  largest  puffballs  may  produce  twenty 
million  million  spores.    The  spores  are  extremely  small  and 


232 


AGRONOMY 


light  and  may  float  in  the  air  for  long  distances  before  coming 
to  rest,  thus  spreading  the  species  very  widely.  Like  other 
plants,  they  need  warmth  and  moisture  to  grow,  and  increase 
most  rapidly  in  warm,  cloudy  weather.  The  harmful  bacteria 
in  the  soil  may  be  carried  from  one  field  to  another  in  the  dirt 


Fig.  169.   Bacterial  wilt  of  melons 
From  Duggar's  "Fungous  Diseases  of  Plants" 

that  adheres  to  the  feet  of  animals,  on  the  implements  used  in 
stirring  the  soil,  and  even  by  currents  of  water  during  rains. 

Number  of  plant  diseases.  An  immense  number  of  organ- 
isms produce  disease  in  plants,  and  if  these  could  all  live  on 
the  first  species  encountered,  it  is  likely  that  few  plants  of 
any  kind  would  come  to  maturity.  Fortunately  most  plant 
diseases  are  restricted  to  a  single  species  or  a  related  group 


PLANT  DISEASES 


233 


of  species ;  hence  plants  of  one  kind  may  be  grown  without 
danger  close  beside  other  kinds  that  are  diseased.  These 
organisms  that  cause  disease  are  usually  given  the  name  of  the 
effect  they  produce.  Among  the  more  familiar  are  the  rots, 
smuts,  rusts,  mildews,  blights, 
and  wilts.  Often  the  causal 
organisms  are  not  closely  re- 
lated, but  if  they  produce  simi- 
lar effects,  they  are  likely  to  be 
named  accordingly,  just  as  a 
rise  in  temperature  in  man  is 
called  a  fever,  no  matter  what 
its  cause.  Some  of  the  more 
common  plant  diseases  are  men- 
tioned here ;  others  may  be 
found  described  in  the  reports 
of  agricultural  experiment  sta- 
tions and  in  manuals  devoted 
to  the  subject. 

Rots.  Many  kinds  of  fruits 
and  vegetables  are  attacked  by 
rots  which  cause  their  tissues  to 
break  down  into  a  watery  mass 
and  thus  spoil  the  specimen. 
Good  examples  are  found  in  the 
rot  of  apples  and  other  fruits, 
carrots,  cabbage,  and  the  like.  The  wet  rot  of  potatoes  is 
another  familiar  form.  Rots  are  caused  both  by  bacteria 
and    other   fungi. 

Wilts.  The  wilts  are  readily  recognized  from  the  fact  that 
the  leaves  of  the  plant  attacked  begin  at  once  to  droop  and 
soon  after  the  death  of  the  individual  ensues.  In  many  cases 
the  wilting  is  caused  by  the  fungus  growing  in  the  ducts  of 
the  plant  and  thus  shutting  off  its  supply  of  moisture. 


.1 

f 

'^ 

\ 

i 

>fF 

Fig.  170.    Mildew  of  cherry 

From  Duggar's  "  Fungous  Diseases 
of  Plants  " 


234 


AGRONOMY 


Blights.    Blights  affect  the  leaves  of  plants,  often  caus- 
ing them  to  shrivel  as  if  touched  by  fire  and  soon  resulting 

in  their  death.  The 
potato  blight  may 
spread  through  an 
entire  crop  and  effect 
its  ruin  in  two  or 
three  days. 

Leaf  spot.  The 
leaves  of  plants  are 
frequently  attacked 
by  fungi  that  cause 
discolored  spots  in 
the  tissues.  Sometimes  these  are  sufficiently  numerous  to 
cause  the  death  of   the   plant  or   render  it  unfit  for   food. 


Fig.  171.  Mildew  of  peaches 
From  Dugarar's  "  Fungous  Diseases  of  Plants  " 


Fig.  172.   Leaf  spot  on  pear 
From  Duggar's  "  Fungous  Diseases  of  Plants  " 

The  brown  spots  that  appear  on  bean  pods  and  other  fruits 
are   closely  allied  to  the  leaf-spot  diseases. 


PLANT  DISEASES 


235 


Molds  and  mildews.  The  molds  and  mildews  may  be  either 
parasites  or  saprophytes.  As  parasites  they  cover  the  leaves 
of  many  species  with  a  cottony  or  powdery  growth  which  is 


\. 


X 


Fig.  173.    Downy  mildew  on  the  grape 
From  Duggar's  "  Fungous  Diseases  of  Plants  " 

the  plant  body,  or  they  push  into  the  interior  of  the  plant, 
whence  later  their  spores  are  released.  The  plants  are  often 
called  downy  mildews,  to  distinguish  them  from  other  species. 
One  form  of  mildew  is  nearly  always  present  on  the  lilac,  and 


'236 


AGllONOMY 


others  are  common  on  the  grape,  woodbine,  and  willow;  in 
fact,  there  are  few  species  of  cultivated  plants  that  do  not 


Fig.  174.    The  hollyhock  rust 

The  small  dots  are  the  fruiting  bodies  containing  multitudes  of  spores 
From  Dusraar's  "  Fungous  Diseases  of  Plants  " 


harbor  some  form  of  mildew.  The  damping-off  fungus  wliich 
attacks  young  seedlings  at  the  point  where  the  stem  leaves 
the  soil  may  be  included  in  this  group. 


PLANT  DISEASES 


237 


Smuts.  The  smuts  cause  the  black  powdery  masses  that  are 
often  to  be  seen  upon  corn,  oats,  and  other  grains.  They  are 
particularly  fond  of  mem- 
bers of  the  grass  famil^^ 
Their  spores  germmate  in 
spring  soon  after  the  seeds 
of  the  plants  which  they 
infect  begin  to  grow.  Get- 
ting into  the  plant  through 
the  stomata  or  through  a 
break  in  the  tissues,  they 
grow  with  the  growing 
plant  until  seeds  begin  to 
be  formed.  At  this  point 
they  fill  up  the  young  seed 
with  their  own  tissues  and 
soon  produce  a  mass  of 
exceedingly  minute  black 
spores  that  float  away  to 
infect  other  plants,  or  that 
cling  to  the  seeds  of  the 
plants  upon  which  they 
grow,  and  are  transported 
with  them.  The  seeds  of 
oats  are  often  treated  with 
formalin  or  hot  water  to 
destroy  the  spores  before 
they  are  planted. 

Rusts.  The  rusts  cause 
rusty  brownish  or  blackish 
patches  on  the  leaves  and 
stems  of  many  plants.  Fields  of  wheat  or  corn,  late  in  the 
season,  will  furnish  good  examples,  and  others  may  be  found 
in  asparagus  beds.   Often  the  wheat  rust  is  so  abundant  as  to 


Fig.  175.   Anthracnose  of  beans 

From    Duggar's    "Fungous   Diseases    of 
Plants" 


238  AGRONOMY 

ruin  the  crop.  There  are  numerous  species  of  rust,  each  re- 
stricted for  the  most  part  to  a  hmited  number  of  hosts.  One 
of  the  most  remarkable  features  of  their  hfe  history  is  the 
fact  that  two  different  species  of  plants  are  usually  required 
to  complete  their  round  of  existence.  The  wheat  rust  is  found 
in  spring  upon  the  barberry  and  not  until  later  does  it  infect 
the  wheat  plant.  The  corn  rust  grows  first  upon  a  species  of 
oxalis ;  the  apple  rust  upon  coniferous  trees.  Late  in  the 
season  the  rusts  produce  spores  which  last  through  the  whiter 


Fig.  170.    Apples  affected  by  apple  scab 
From  Duggar's  "  Fungous  Diseases  of  Plants  " 

and  set  up  the  infection  upon  the  first  host  plant  again.  It 
occasionally  happens  that  the  first  of  the  two  plants  necessary 
for  a  complete  life  cycle  of  a  rust  is  absent  from  the  locality. 
In  this  event  most  species  are  able  to  omit  this  part  of  the 
cycle  and  begin  at  once  upon  the  second  host.  Many  rusts 
produce  no  less  than  four  different  kinds  of  spores. 

Wound  parasites.  Many  enemies  of  the  woody  plants  are 
fungi  that  gain  entrance  through  wounds,  as  where  a  branch 
has  been  torn  off  by  the  wind,  or  through  a  break  in  the  bark 
caused  by  insects  or  mammals.  These  parasites  live  upon  the 
old  parts  of  the  tree  until  well  established,  but  ultimately 
extend  to  the  livmg  parts  and  cause  their  death.    Often  their 


PLANT  DISEASES 


239 


presence  is  not  suspected  until  the  spore-bearing  parts  appear, 
and  then  it  is  too  late  to  eradicate  them.  The  oyster  mush- 
room and  some  of  the  shelf  fungi  are  among  the  better  known 
of  the  wound  parasites.  The  entrance  of  such  parasites  may- 
be prevented  by  promptly  covering  all  wounds  with  paint 
or  grafting  wax. 

Other  plant  diseases.    The  list  of  plant  diseases  is  a  very 
long  one.    It  includes  the  black  knot  on  plum,  fire  blight  of 


I'lG,  177.   Potatoes  affected  by  potato  scab 
From  Duggar's  "Fungous  Diseases  of  Plants" 

the  apple  and  pear,  peach  yellows,  plum  pockets,  potato  scab, 
cedar  apples,  witches'-brooms,  peach-leaf  curl,  clubroot  of 
cabbage,  anthracnoses,  and  a  host  of  others.  It  is  usually  not 
necessary  to  positively  identify  the  organism  causing  the  dis- 
ease in  order  to  remedy  it,  since  what  will  control  one  disease 
will  be  likely  to  control  all  the  others  like  it.  The  main  thing 
is  to  discover  the  trouble  before  it  has  had  time  to  spread,  and 
to  take  prompt  measures  for  its  suppression.  In  a  majority 
of  cases  the  most  efficient  treatment  is  to  spray  with  some 


240  AGRONOMY 

good  fungicide,  meanwhile  removing  all  affected  plants  if  the 
disease  has  progressed  very  far. 

Sprays  and  spraying.  The  spray  to  be  used  for  fungi  de- 
pends partly  upon  the  time  of  the  year  in  vv^hich  it  is  applied, 
and  partly  upon  the  kind  of  fungus  to  be  exterminated.  When 
the  plants  are  leafless  and  dormant,  the  lime  and  sulphur  wash 
is  the  one  to  be  applied,  while  the  Bordeaux  mixture  and  the 
ammoniacal  copper  carbonate  solution  may  be  used  as  the  buds 
begin  to  open  and  at  intervals  throughout  the  summer.  As 
yet  there  is  no  known  remedy  against  some  plant  diseases. 
Fire  blight  of  the  apple  and  pear,  in  which  the  branches  die 
from  the  tip  inward  as  if  touched  by  fire,  is  one  of  these.  The 
only  way  to  save  specimens  attacked  by  it  is  to  cut  out  the 
blight  a  foot  or  more  below  the  part  affected  as  soon  as  it 
appears.  As  a  general  thing,  internal  parasites  are  not  injured 
by  sprays,  though  they  may  be  kept  from  spreading  by  such 
means.  External  parasites  are  usually  killed  outright.  When 
in  doubt  as  to  the  proper  spray  to  use,  it  is  a  good  rule  to 
choose  Bordeaux.  Powdered  sulphur  sprinkled  upon  the  leaves 
is  also  of  use,  especially  in  combating  mildew. 

Bordeaux  mixture.  The  spray  mixture  adapted  to  the  great- 
est variety  of  uSes  is  undoubtedly  Bordeaux  mixture,  made 
from  lime  and  copper  sulphate  or  "bluestone."  A  standard 
mixture  consists  of  5  pounds  of  copper  sulphate,  5  pounds 
of  lime,  and  50  gallons  of  water.  To  make  it,  the  lime  and 
copper  sulphate  are  dissolved  in  a  little  water  in  separate 
receptacles,  and  then  further  diluted  with  about  half  of  the 
50  gallons  before  mixing.  If  mixed  without  diluting,  it  makes 
a  thick  curdled  mass  that  does  not  readily  mix  with  the  water. 
When  properly  mixed  the  liquid  should  be  of  a  brilliant,  sky- 
blue  color.  Three  or  four  pounds  of  soap  are  sometimes  added. 
The  lime  in  this  mixture  is  chiefly  used  to  neutralize  the 
copper  sulphate,  and  it  should  always  be  in  excess  of  the 
quantity  needed  for   this.    The  solution  may  be  tested  by 


PLANT  DISEASES 


241 


dipping  into  it  any  bright  piece  of  steel.  If  it  has  a  coating  of 
copper  upon  it  when  withdrawn,  more  lime  should  be  added. 
Another  test  is  to  put  a  few  drops  of  potassium  ferrocyanide 
into  a  little  of  the  solution.  If  it  turns  brick  red,  more  lime 
is  needed.  If  the  potassium  ferrocyanide  remams  yellow,  suffi- 
cient lime  is  present.  An  excess  of  lime  does  no  harm.  The 
mixture  here  described  is  often  known  as  the  5-5-50  solution, 
the  numbers  referring  to  the  quantity  of  each  ingredient 
employed.  Other 
proportions  may 
be  taken :  the 
4-4-50  and  the 
3-3-50  are  pop- 
ular. The  mix- 
ture should  be 
strauied  before 
using.  This  spray 
does  not  poison 
insects,  and  if  a 
poison  is  desired 
with  it,  arsenate 
of  lead  in  the  pro- 
portion of  two 
or  three  pounds 
to  fifty  gallons  may  be  added.  Copper  sulphate  is  often  used 
alone  with  water  in  the  proportion  of  one  pound  to  twenty 
gallons.  This  can  be  used  only  before  the  buds  open,  never 
on  the  leaves. 

Lime-sulphur  wash.  For  spraying  all  woody  plants  in 
the  dormant  condition,  the  lime-sulphur  wash  is  preferred. 
It  consists  of  fifteen  pounds  each  of  lime  and  sulphur  and 
fifty  gallons  of  water.  To  make  it,  bring  the  water  to  the 
boiling  point  and  add  the  lime.  Make  a  paste  with  the  sul- 
phur and  a  small  quantity  of  hot  water,  add  to  the  boilmg 


-mm 

I'liotograph  by  Bateman  Manufacturing  Co. 

Fig.  178.    Spraying  a  young  fruit  tree  by  means  of  a 
bucket  pump  sprayer 


242 


AGRONOMY 


mixture,  and  continue  boiling  for  about  half  an  hour.  Five 
or  ten  pounds  of  salt  is  often  added  while  boilbig.  This 
mixture  does  not  keep  and  should  be  used  as  soon  as  made. 
The  wash  may  also  be  made  by  taking  double  tlie  quantity 
of  lime,  slaking  it  with  boiling  water,  and  adding  tlie  sulphur 
while  still  hot ;  or  the  heat  developed  by  the  lime  in  slakmg 
may  be  sufficient.    This  latter  is  called  the  unboiled  wash. 


Fig.  179.   Potato  field  attacked  by  late  blight,  showing  the  difference 
between  sprayed  and  unsprayed  rows 

From  Duggar's  "  Fungous  Diseases  of  Plants" 

Ammoniacal  copper  carbonate.  This  spray  is  made  by  add- 
ing five  ounces  of  copper  carbonate  and  three  pints  of  am- 
monia to  about  fifty  gallons  of  water.  A  paste  is  first  made 
with  the  copper  carbonate  and  a  little  water,  the  ammonia  is 
added,  and  then  the  rest  of  the  water.  The  mixture  should 
stand  until  it  settles,  and  only  the  clear  liquid  on  top  should 
be  used.  This  spray  is  effective  against  rusts,  leaf  spots,  and 
blights. 


PLANT  DISEASES  243 

Potassium  sulphide  solution.  The  potassium  sulphide  solu- 
tion is  made  by  mixing  one  ounce  of  liver  of  sulphur  with 
three  gallons  of  water.  It  is  used  as  soon  as  made,  and  is  an 
excellent  remedy  for  mildews. 

Preventive  measures.  Since  few  plant  diseases  can  be  com- 
pletely cured  and  many  are  only  held  in  check  with  difficulty, 
it  is  wise  to  take  every  precaution  against  the  entry  of  dis- 
ease. Some  plants  are  more  resistant  than  others  of  the  same 
species,  and  these  should  be  grown.  In  some  cases  it  seems 
possible  to  breed  up  a  resistant  strain.  Disease  always  attacks 
the  less  thrifty  individuals  first.  Plants  should  be  kept  in 
good  health  by  proper  cultivation  and  thus  rendered  more 
resistant.  Diseased  plants,  when  they  occur,  should  be  removed 
and  burned.  If  allowed  to  remain,  they  only  spread  the  trouble 
to  other  healthy  individuals.  Burning  the  plants  kills  the 
spores  that  might  otherwise  set  up  new  areas  of  infection. 

PRACTICAL  EXERCISES 

1.  List  the  plant  diseases  known  to  be  in  your  locality.  Underscore 
the  most  destructive. 

2.  Tear  apart  decaying  logs  and  examine  the  white  threadlike 
growths  which  form  tlie  plant  body  of  the  higher  fungi.  See  if  you 
can  trace  the  fruiting  parts  of  puffballs,  mushrooms,  and  shelf  fungi 
to  such  plant  bodies. 

3.  Examine  the  "smoke"  from  a  puffball  with  microscope.  The 
small  objects  seen  are  spores.    Draw  several. 

4.  Make  a  spore  print  by  placing  the  cap  or  top  of  a  mushroom, 
with  gills  down,  upon  a  piece  of  clean  paper.  Cover  with  a  bell  jar  or 
drinking  glass  for  a  day.  The  spores  will  be  discharged  in  immense 
quantities.  Some  species  have  white  spores,  and  these  will  show  best  if 
colored  paper  is  used. 

5.  Make  a  collection  of  leaves  and  stems  to  show  rusts,  mildews, 
leaf  sjiots,  and  smuts.  These  should  be  preserved,  with  proper  labels,  for 
the  use  of  other  classes. 

6.  Scrape  off  some  spores  from  specimens  affected  with  rust  and 
examine  with  the  microscope.  The  summer  spores  are  one  celled,  but 
the  winter  spores  are  usually  two  or  several  celled. 


244  AGRONOMY 

7.  Remove  some  of  the  ascocarps  of  lilac  mildew  from  a  lilac  leaf 
(they  api>ear  to  the  unaided  eye  like  small  black  si)ecks)  and  examine 
with  the  microscof)e.  Compare  with  the  fruiting  parts  of  any  other 
mildew  you  can  find.  Crush  the  ascocarps  to  see  ascospores  and  asci. 
Make  a  collection  of  mildewed  leaves.  The  fruiting  bodies,  or  ascocarps, 
are  likely  to  be  mature  in  late  summer. 

8.  Make  a  collection  of  the  fungi  that  grow  on  wood. 

9.  Visit  museums  for  other  kinds  of  fungi. 

10.  Make  a  collection  of  the  different  ingredients  used  in  making 
insect  sprays. 

11.  Make  up  standard  solutions  of  the  various  sprays  and  use  in  the 
garden.  If  no  plants  there  need  sjjraying,  spray  those  that  are  most 
likely  to  need  it. 

12.  Visit  a  hardware  or  implement  store  and  study  the  various  forms 
of  sprayers  in  stock. 

References 

Bailey,  "Manual  of  Gardening." 

Duggar,  "  Fungous  Diseases  of  Plants." 

Stevens  and  Hall,  "  Diseases  of  Economic  Plants." 

Farmers'  Bulletins 

75.  The  Grain  Smuts. 

146.  Insecticides  and  Fungicides. 

227.  Lime-Sulphur-Salt  Wash. 

2.31.  Spraying  for  Cucumber  and  Melon  Wilt. 

24.3.  Fungicides. 

259.  Disease-Resistant  Crops. 

Bureau  of  Plant  Industry 

17.  Some  Diseases  of  the  Cowpea. 

76.  Copper  as  an  Insecticide. 

171.  Some  Fungous  Diseases  of  Economic  Impoilance. 


CHAPTER  XVII 

INSECT  PESTS 

How  insects  injure  plants.  After  the  young  plants  have 
broken  through  the  soil  with  every  indication  of  becoming 
thrifty  and  fruitful  specimens,  or  after  older  and  well-estab- 
lished plants  have  given  indications  of  an  abundant  crop,  a 
multitude  of  fungous  and  insect  pests  have  still  to  be  reckoned 
with  by  the  gardener  before  a  return  for  his  labor  is  assured. 
Nearly  all  the  insects  that  prey  upon  cultivated  plants  are  so 
voracious  and  multiply  in  such  numbers  that  the  crop  is  some- 
times destroyed  in  spite  of  every  effort  of  the  gardener  to  pre- 
vent it.  It  is  estimated  that  insects  and  plant  diseases  cause 
more  than  a  billion  dollars'  damage  to  crops  each  year.  As 
regards  the  way  in  which  they  injure  crops,  insects  may  be 
divided  into  two  groups  —  those  with  mouth  parts  adapted  to 
chewing,  and  those  with  mouth  parts  adapted  to  sucking.  The 
chewing  insects  harm  the  plants  by  eating  stems  and  foliage, 
or  by  burrowing  into  fruits,  stems,  and  other  plant  parts.  The 
sucking  insects  do  not  defoliate  the  plant,  but  by  sucking  the 
juices  from  the  tender  tissues  they  are  nearly  or  quite  as  harm- 
ful. Chewing  insects  may  be  controlled  by  poisons,  but  such 
substances  have  no  effect  upon  sucking  insects  whose  food 
comes  entirely  from  the  interior  of  the  leaf.  These  latter  must 
be  fought  with  smothering  sprays  and  gases. 

Metamorphoses  of  insects.  There  are  two  general  lines  along 
which  insects  develop  from  the  egg  to  maturity.  In  grasshop- 
pers, crickets,  katydids,  and  the  like,  the  newly  hatched  insect 
has  considerable  resemblance  to  adult  forms  and  gradually 
acquires  the  characters  of  maturity  as  it  grows  in  size.    Such 

245 


246  AGRONOMY 

insects  are  said  to  liave  an  incomplete  metamorphosis.  The 
great  majority  of  insects,  however,  have  a  complete  metamor- 
phosis. When  hatched  they  show  no  sign  of  the  kind  of  adult 
insects  they  are  designed  to  be.  They  begin  life  as  wormlike 
creatures  called  caterpillars  or  worms,  though  it  should  be 
understood  that  they  are  not  closely  related  to  the  true  worms, 
such  as  the  earthworm.  The  young  worms,  or  more  properly 
the  larvcBy  feed  voraciously  until  they  reach  maturity,  mcreas- 
ing  rapidly  in  size  and  casting  their  skins  from  time  to  time 
as  these  become  too  small.  When  full-grown  they  stop  feed- 
ing and  either  spin  a  cocoon  about  themselves  or  creep  away 
into  some  safe  shelter  under  a  loose  piece  of  bark,  along  old 
fences,  or  even  in  the  soil,  where  they  remain  motionless 
for  several  days,  weeks,  or  months,  during  which  time  they 
undergo  great  changes  in  form  and  structure.  This  stage  is 
called  the  pupa  stage  and  is  the  one  in  which  large  numbers 
pass  the  winter.  At  length  there  emerges  from  the  dull  and 
motionless  pupa  a  winged  insect,  often  brightly  colored, 
which  flies  away  to  mate  and  deposit  eggs  upon  the  proper 
food  plant  and  thus  start  the  life  cycle  anew. 

Forms  of  insects  that  cause  injury.  Crops  may  be  mjured 
by  insects  in  either  the  larval  or  adult  stage.  An  insect  is 
seldom  equally  harmful  in  both  stages.  Usually  the  greatest 
damage  is  caused  by  the  voracious  larvse,  the  mature  insects 
often  living  on  the  nectar  of  flowers  and  frequently  being 
beneficial  as  agents  for  the  transfer  of  the  pollen.  In  some 
cases  the  larvae  are  much  less  destructive  than  the  mature 
insects,  possibly  because  they  feed  on  plants  that  are  not 
valued  by  man,  while  others,  like  the  potato  bug  and  the 
asparagus  beetle,  in  both  their  larval  and  adult  stages  are 
mjurious  to  crops.  Some  of  the  more  harmful  insects  are 
mentioned  in  this  book.  ]\Iany  others,  less  widely  distributed, 
though  often  as  destructive  in  restricted  localities,  may  be 
found  in  any  work  on  entomology.    As  with  plant  diseases, 


INSECT  PESTS  247 

it  is  usually  not  necessary  to  identify  the  exact  species  that 
causes  the  damage.  It  is  sufficient  to  know  how  they  injure 
the  crops  and  to  be  able  to  adopt  the  methods  that  will  most 
readily  exterminate  them. 

Cutworms.  Cutworms  are  dull,  earth-colored,  or  striped 
worms  that  seek  refuge  in  the  soil  during  the  day,  coming  out 
at  night  to  feed.  They  cause*  immense  losses  to  many  culti- 
vated crops,  cutting  off  the  young  seedlings  just  as  they  appear 
aboveground  and  often  following  along  a  row  until  all  the 
plants  are  taken.  Some  climbing  species  creep  up  the  stems 
of  plants  and  cut  off  their  tops  or  even  ascend  trees  to  feed  on 
the  buds.  In  some  grounds  they  occur  in  great  numbers.  Two 
hundred  or  more  have  been  taken  out  of  a  single  row  sixty 
feet  long.  They  are  very  hard  to  exterminate,  owing  to  their 
nocturnal  habits  and  manner  of  hiding,  but  they  may  some- 
times be  killed  by  putting  poisoned  food  about  their  haunts. 
Clover,  pigweed,  or  other  tender  vegetation  sprayed  with 
poison  makes  attractive  bait.  Cabbage,  tomato,  and  other  plants 
grown  singly  may  be  protected  by  a  collar  of  stiff  paper  about 
the  stems  at  the  surface  of  the  ground.  When  evidences  of 
the  Avork  of  cutworms  is  seen,  the  worms  should  be  dug  out 
and  killed.  This  is  easy,  since  they  do  not  go  very  far  to  hide 
during  the  day.  One  method  of  keeping  them  in  check  is  to 
pick  them  by  hand  at  night  by  the  light  of  a  lantern.  The  half- 
grown  cutworms  spend  the  winter  in  the  earth,  and  cultivating 
the  soil  up  to  the  time  of  frost  tends  to  reduce  their  num- 
bers. The  mature  insect  is  a  dull-colored  moth  of  nocturnal 
habits  and  is  seldom  recognized. 

Cabbage  worm.  The  cabbage  worm  is  a  light  green,  smooth 
worm  that  infests  cabbage,  cauliflower,  turnip,  and  other  plants 
of  the  cress  family.  It  feeds  on  the  leaves,  and  when  resting 
extends  along  the  veins,  which  it  so  closely  resembles  as  to 
be  frequently  overlooked.  The  worms  may  be  easily  poisoned. 
This  does  not  injure  the  cabbage  for  food,  since  the  leaves  are 


248  AGRONOMY 

wrapped  in  such  a  way  that  the  poison  cannot  penetrate  to 
the  edible  portion  of  the  head.  The  small  white  butterfly,  so 
common  in  cabbage  patches,  is  the  mature  form  of  this  species. 

Currant  worm.  Two  broods  of  the  currant  worm  occur 
annually  :  the  first  appears  before  the  fruit  is  ripe ;  the  second 
about  midsummer.  The  currant  worm  is  a  green-  and  black- 
spotted  larva  and  so  voracious  that  a  small  colony  will  defo- 
liate a  currant  or  gooseberry  bush  in  a  very  short  time  if  not 
checked.  It  is  easily  controlled  by  poisons,  white  hellebore 
being  one  of  the  best  for  use  in  small  gardens. 

Tomato  worm.  The  tomato  worm  is  a  very  large,  smooth 
green  worm  with  a  hornlike  projection  at  one  end  and  oblique 
white  markings  on  its  sides.  On  account  of  its  large  size  it  is 
easily  located  by  the  gardener  and  falls  an  easy  prey  to  para- 
sitic insects.  It  passes  the  pupa  stage  in  the  earth  and  is  often 
dug  up  when  the  ground  is  spaded  in  spring.  At  this  stage  it 
may  be  identified  by  a  curved  projection  extending  down  one 
side  like  a  handle.  At  maturity  it  becomes  one  of  the  sphinx 
or  humming-bird  moths  often  seen  about  long-tubed  flowers 
in  the  late  afternoon.  A  related  species  does  much  damage 
to  crops  of  tobacco. 

Corn-ear  worm.  The  corn-ear  worm  is  closely  allied  to  the 
cutworms  and  army  worms,  but  is  found  on  or  within  the  re- 
productive parts  of  the  corn  plant.  It  destroys  the  tassel  by 
eating  it  off,  and  later  creeps  down  into  the  ear  between  the 
husks  and  the  cob,  eating  the  kernels  as  it  goes  and  ruinmg  the 
ear  for  food.   There  is  no  known  preventive  for  it  at  present. 

Tent  caterpillar.  The  webworms,  or  tent  caterpillars,  are 
readily  recognized  by  the  webs  they  spin  on  trees  and  bushes 
and  within  which  they  feed.  These  webs  may  be  removed  and 
the  insects  destroyed  by  burning  them  out  with  a  torch  made 
of  a  piece  of  cloth  wound  about  the  end  of  a  pole  and  saturated 
with  kerosene.  A  corncob  soaked  in  oil  and  fastened  to  a  pole 
also  makes  a  good  torch. 


INSECT  PESTS  249 

Codlin  moth.  The  larva  of  the  codliii  moth  is  a  small  white 
worm  that  is  often  discovered  feeding  in  the  fruit  of  the  apple. 
The  mature  insect  lays  her  eggs  in  the  blossoms  and  the  very 
young  fruit,  and  after  the  larva  hatches  out  it  enters  the  fruit, 
usually  at  the  blossom  end.  To  prevent  its  depredations  the 
trees  must  be  sprayed  as  soon  as  the  petals  fall  and  while  the 
calyx  is  still  open. 

Curculio.  The  curculio  is  a  small  white  worm  that  inhabits 
the  fruit  of  the  peach,  plum,  cherry,  and  similar  species.  The 
eggs  are  inserted  just  beneath  the  skin  of  the  young  fruit,  and 
the  worm  hatches  out  and  feeds  upon  the  pulp.  Poisons  have 
no  effect  upon  the  worm,  but  the  trees  may  be  sprayed  with 
poisons  to  protect  them  from  the  mature  insect.  Peaches,  how- 
ever, and  stone  fruits  in  general,  are  very  sensitive  to  sprays, 
and  instead  of  using  such  methods  the  trees  may  be  jarred 
every  morning  for  some  days  after  flowering  and  the  insects 
caught,  as  they  fall  from  the  trees,  and  burned. 

Cankerworms.  The  cankerworms  are  also  called  inchworms, 
measuring  worms,  and  spanworms.  They  eat  the  foliage  of 
many  plants,  and,  when  disturbed,  drop  to  the  ground  on  the 
end  of  a  long  thread  which  they  spin.  The  pupa  stage  is 
passed  in  the  soil.  The  female  is  wingless  and  climbs  the 
trees  to  lay  her  eggs.  Her  ascent  may  be  stopped  by  a  band 
of  cloth  or  cotton  around  the  trunk.  Beneath  this  she  will 
hide  and  may  then  be  caught  and  killed. 

Borers.  Numerous  species  of  borers  infest  the  trunks  of 
trees  and  occasionally  other  parts  as  well.  They  make  their 
burrows  in  the  wood  and  bark,  weakening  the  stem,  destroy- 
ing the  cambium,  and  causing  the  death  of  the  tree.  Their 
presence  is  indicated  by  small  mounds  of  fine  wood  dust 
about  the  base  of  the  trees,  or  by  the  gum  that  oozes  out  of 
the  wounds  in  some  species.  Borers  should  be  cut  out  as  soon 
as  discovered,  or  killed  by  pushing  a  stout  wire  into  their 
burrows  until  it  crushes  them.   In  some  cases  a  few  drops  of 


250  AGRONOMY 

carbon  disulphide  injected  into  their  burrows  with  a  small  oil 
can,  and  the  opening  afterwards  plugged  up,  is  effective. 

Elm-leaf  beetle.  The  elm-leaf  beetle  is  a  small  beetle  that 
destroys  the  leaves  on  elm  trees.  It  is  very  destructive,  but 
at  present  is  practically  confined  to  the  New  England  States. 
It  may  be  controlled  by  sprays. 

Cucumber  beetle.  The  cucumber  beetle  is  a  small  yellow- 
and  black-striped  insect  that  is  very  destructive  to  cucumbers, 
melons,  and  allied  plants  by  eating  the  leaves  of  the  seedlings. 
The  young  plants  are  sometimes  protected  by  frames  covered 
with  screen,  or  they  may  be  sprayed  with  poisons  or  dusted 
with  white  hellebore. 

Blister  beetles.  The  blister  beetles  are  long-necked,  black 
or  gray  insects  that  feed  on  the  foliage  and  flowers  of  many 
species.  They  very  frequently  injure  the  flowers  of  composite 
plants,  such  as  asters,  by  eating  the  ray  flowers.  Hand  picking 
and  spraying  with  poisons  are  the  only  remedies. 

Potato  beetle.  The  potato  beetle  is  more  commonly  known 
as  the  potato  bug.  The  mature  insect  is  a  nearly  hemispheri- 
cal creature  with  pale  yellow  and  black  stripes, 
and  the  larva?  are  repulsive-looking  red  objects 
with  black  markings.  This  insect  is  usually 
most  abundant  on  potato  plants,  the  foliage 
of  which  is  eaten  by  both  the  larvsB  and  the 
mature  insects.    Usually  the  plants  are  soon 

killed  if  they  are  not  protected.    Hand  pick- 
A  potato  beetle      .  •'  .  •  i     r»     .  , 

mg  and  spray mg  with  Paris  green   or  other 

poisons  will  keep  the  pest  within  bounds. 

May  beetles.    The  larvae  of  the  iNIay  beetle  or  June  bug  are 

the  whitish  grubs  common  in  grasslands  and  not  infrequently 

found  in  cultivated  fields  as  well.    They  feed  underground 

and  often  do  much  damage  by  eating  the  roots  of  plants.   The 

mature  insect  is  a  brownish  beetle  familiar  to  all  by  its  habit 

of  buzzing  around  the  lights  in  spring. 


mSECT  PESTS  251 

Plant  lice,  or  aphids.  Plant  lice  are  small,  usually  wing- 
less insects,  black,  green,  orange,  or  white  in  color,  that  are 
found  on  the  stems,  the  underside  of  the  leaves,  and  even  on 
the  roots  of  plants.  They  increase  in  number  with  incredible 
rapidity,  and  when  a  colony  gets  crowded,  wmged  individu- 
als are  produced  that  may  spread  the  species  to  other  plants. 
They  suck  the  juice  from  the  tender  parts  and  weaken  or  kill 
the  plants  upon  which  they  are  allowed  to  thrive.  One  species 
that  frequents  lettuce,  peas,  and  other  cultivated  crops  is  known 
as  the  green  fly  or  green  bug.  Plant  lice  excrete  a  sweetish 
fluid  that  is  greatly  relished  by  ants,  and  the  latter  may  usu- 
ally be  found  in  attendance  upon  them.  Ants  also  contribute 
to  the  spread  of  the  aphids  by  carrymg  some  of  tliem  off  to 
new  pastures  when  the  colony  on  a  given  leaf  becomes  crowded. 
The  attendant  ant  of  the  corn-root  louse  actually  carries  the 
aphids  off  to  a  safe  place  and  cares  for  them 
until  the  corn  is  up  and  then  places  them  on 
the  roots  of  the  young  plants,  where  they 
spend  the  rest  of  the  summer. 

Squash  bug.  The  squash  bugs  are  large 
angular  insects  found  on  the  underside  of  the 
leaves  of  squash,  pumpkin,  and  the  like.  They  ^     .g, 

have   an   exceedingly  disagreeable  odor  and        ^  squash  bu"- 
are  commonly  known  as  "  stinkbugs."    The 
egg  masses  are  conspicuous  as  large,  shining  brown  patches 
and  may  be  gathered  by  hand  and  burned.   Kerosene  emulsion 
may  be  used  as  a  spray  for  the  mature  insects. 

Mealy  bug.  House  plants  and  the  specimens  of  the  florist 
often  become  infested  with  mealy  bugs.  These  are  small 
fuzzy  insects,  white  in  color,  that  suck  the  juices  from  plants 
and  are  hard  to  exterminate  because  ordinary  sprays  do  not 
harm  them.   No  absolutely  certain  remedy  seems  to  be  known. 

Scale  insects.  In  appearance  scale  insects  are  minute  scale- 
like objects  clinging  close  to  the  bark  of  young  trees  of  many 


252 


AGRONOMY 


Fig.  182.  Scale  insects  on 
a  maple  leaf 


kinds,  often  covering  every  available  spot.  The  scale  is  a 
waxy  substance  secreted  by  the  insect,  and  under  tliis  it  lives, 
sucking  the  juice  from  the  tree  and  multiplying  rapidly.  If 
not  eradicated,  it  will  ultimately  cause  the  death  of  the  plant. 
Strong  sprays  that  can  be  used  when 
the  plant  is  dormant  are  most  useful  in 
combating  this  pest.  The  lime-sulphur 
spray  used  against  fungous  pests  is  also 
effective  against  this  one,  although  it 
can  be  used  in  winter  only. 

Preventing  attacks  of  insects.  It  is 
more  difficult  to  protect  plants  from 
winged  insects  than  from  creeping  ones, 
since  the  former  can  go  from  one  plant 
to  another  through  the  air.  Creeping 
insects  may  be  trapped  or  repelled  in 
numerous  ways.  The  foliage  of  plants 
likely  to  be  attacked  may  be  sprinkled  with  ashes  or  slaked 
lime.  Bands  of  sticky  paper  or  tar  may  check  the  advances 
of  climbing  species,  and  whitewashing  the  trunks  of  trees  will 
discourage  many  others.  Small  plants  may  be  screened,  but, 
in  general,  poisons  and  sprays  are  most  effective.  Bands  of 
cotton  fastened  about  the  trunks  of  trees  some  distance  from 
the  ground  are  favorite  hiding  places  for  many  insects,  which 
may  thus  be  easily  caught  and  killed. 

Poisons  for  chewing  insects.  For  all  kinds  of  chewing  insects 
one  of  the  poisons  adapted  to  the  purpose  should  be  used.  Of 
these  the  most  useful  for  general  purposes  in  the  small  garden 
is  ivhite  hellebore,  which  may  be  procured  at  any  drug  store. 
This  may  be  sprayed  on  the  infested  plants  in  the  proportion 
of  1  ounce  to  3  gallons  of  water,  or  it  may  simply  be  dusted 
on  the  foliage  when  wet  with  the  dew.  White  hellebore  is 
not  so  poisonous  as  some  of  the  other  remedies  used,  but 
its   convenience    serves    to   recommend    it.    Paris   green,   an 


INSECT  PESTS 


253 


aceto-arsenite  of  copper,  is  a  dry  green  powder  extensively 
used  upon  field  crops.  It  is  made  up  in  various  strengths 
with  water,  1  pound  to  150  gallons  being  near  the  average. 
When  used  on  stone  fruits  it  is  made  much  weaker,  while  for 
potatoes  it  is  used  stronger.  In  preparing  it  the  poison  is 
formed  into  a  paste  with  3  or  4  pounds  of  lime  and  a  little 
water  and  is  then  diluted  to  the  proper  degree.    The  foliage 


riiotograph  byBateniaa  Mauuiaetiirm^  Co. 

Fig.  183.   Spraying  trees  in  winter  to  destroy  scale  insects 


of  many  plants  is  injured  by  Paris  green,  and  it  is  gradually 
being  replaced  by  arsenate  of  lead,  which  does  not  have  this 
defect.  Arsenate  of  had  is  a  white  pasty  mixture  that  may 
be  purchased  of  dealers  in  seeds  or  drugs.  It  is  used  as  a 
spray  in  the  proportion  of  2  or  3  pounds  to  50  gallons  of 
water.  The  poison  sticks  well  and  does  not  injure  the  foliage, 
two  qualities  which  make  it  desirable.  Poisons  should  not  be 
left  where  children  and  farm  animals  may  find  them. 


254  AGKONOMY 

Remedies  against  sucking  insects.  Poisonous  sprays  have 
no  effect  upon  insects  whicli  suck  the  juices  out  of  plants. 
These  insects  must  be  killed  by  suffocating  them  in  various 
ways.  One  of  the  best  and  cheapest  insecticides  for  this  pur- 
pose is  Persian  insect  powder,  for  sale  by  all  druggists.  It  may 
be  applied  by  means  of  a  small  bellows,  and  is  very  efficient  in 
clearing  insects  out  of  small  crevices  where  sprays  have  diffi- 
culty in  penetrating.  The  standard  spray  is  kerosene  emulsion^ 
made  by  adding  2  gallons  of  kerosene  to  1  gallon  of  hot 
soft  water  in  which  half  a  pound  of  soap  has  been  dissolved. 
This  is  then  very  thoroughly  churned  in  order  to  make  an 
emulsion  that  will  mix  with  water.  When  wanted  for  use, 
it  is  diluted  with  from  10  to  30  gallons  of  soft  water.  The 
strong  solutions  are  used  for  scale  insects ;  the  weaker  ones 
for  plant  lice.  Whale-oil  soap  is  often  used  for  house  plants 
and  greenhouse  specimens.  The  spray  is  made -by  dissolving 
2  pounds  of  whale-oil  soap  in  1  gallon  of  soft  water.  A  strong 
soapsuds,  made  from  any  kind  of  soap  (naphtha  soap  pre- 
ferred), is  also  useful.  Tobacco  water  is  made  by  pouring  hot 
water  over  a  quantity  of  tobacco  stems  and  allowing  them  to 
steep  for  several  hours.  This  liquid  is  then  diluted  and  used 
as  a  spray.  In  plant  houses,  cold  frames,  and  the  like,  tobacco 
smoke  is  often  relied  upon  for  killing  aphids.  Carbon  disulphide, 
which  may  be  purchased  of  the  druggist,  is  an  ill-smelling 
liquid  that  turns  to  gas  as  soon  as  exposed  to  the  air.  It  is 
heavier  than  air  and  may  be  used  to  exterminate  ants  and 
other  vermin  that  burrow  underground.  A  little  of  the  liquid 
is  poured  into  the  entrance  of  the  burrow,  which  is  then 
stopped  up.  Carbon  disulphide  is  very  inflammable  and  should 
not  be  used  where  there  are  fires  of  any  kind.  In  the  larger 
operations  of  the  horticulturist  hydrocyanic  gas  is  sometimes 
used.  It  is  a  deadly  poison  and  must  be  handled  with  great 
caution.  In  fumigating  with  this,  a  tentlike  covering  is  placed 
about  the  entire  plant  and  filled  with  the  gas. 


INSECT  PESTS  255 

Spray  pumps.  Many  kinds  of  spray  pumps  designed  to 
throw  liquid  upon  the  plants  in  minute  droplets  are  for  sale 
by  dealers.  Sprayers  or  atomizers  quite  effective  enough  for 
small  gardens  may  be  had  for  as  little  as  fifty  cents.  Some 
pumps  may  be  used  with  an  ordinary  bucket,  and  others  are 
carried  like  a  knapsack.  For  large  fields  spray  pumps  drawn 
by  horses  are  used.  In  lieu  of  a  spray  pump  the  liquids  may 
be  sprinkled  on  the  plants  by  hand,  using  a  bunch  of  twigs 
or  a  whisk  broom  for  the  purpose. 

Other  aids  in  fighting  insects.  Although  insects  often  mul- 
tiply prodigiously  and  may  suddenly  become  exceedingly 
numerous  in  a  locality,  it  is  seldom  that  an  unusual  increase 


iiaigBmtmmmii^^ 


Fig.  184.    A  good  form  of  hand  sprayer 

is  long  maintained.  The  number  of  insects  averages  about 
the  same  from  year  to  year.  This  is  doubtless  due  to  the  fact 
that  each  species  has  its  own  natural  enemies,  and  when  it 
becomes  abundant,  the  species  that  prey  upon  it  also  become 
more  numerous  and  soon  reduce  it.  One  of  the  most  powerful 
of  these  enemies  is  the  common  toad.  This  animal  lives  entirely 
upon  insects  and  is  not  very  particular  as  to  the  kind.  In  the 
course  of  a  single  summer  it  destroys  many  thousands  of 
harmful  ones.  Small  snakes  also  live  upon  insects  and  mice, 
while  the  usefulness  of  birds  as  insect  eaters  is  well  known. 
A  large  number  of  the  latter,  among  which  are  the  wood- 
peckers, swallows,  warblers,  vireos,  and  wrens,  are  entirely 
insectivorous,  while  others  that  eat  some  seeds  make  insects 


256 


AGROXOMY 


Fig.  185.    Ladybng 

Showing  larvae  and  mature 
insect 


the  bulk  of  their  diet,  seeming  to  prefer  them  to  seeds.  Even 
those  listed  as  true  seed  eaters  do  not  feed  to  any  great  extent 
upon  the  seeds  of  cultivated  plants,  and 
usually  feed  their  young  upon  insects.  In- 
sects also  have  their  contagious  diseases, 
and  may  be  exterminated  by  spreading 
the  infection  among  them.  Last,  but  by 
no  means  least,  are  the  insects  that  prey 
upon  others.  The  dragon fiy,  often  called 
the  mosquito  hawk,  feeds  almost  exclu- 
sively upon  mosquitoes  ;  the  tiger  beetle 
attacks  and 
kills  many 
kinds  of  in- 
sects; the  ant  lion  preys  upon 
ants ;  ground  beetles  eat  the  eggs 
of  other  species ;  the  spider  cap- 
tures flies,  grasshoppers,  crickets, 
and  the  like ;  and  certain  wasps 
stock  the  larder  for  their  young 
with  captured  flies.  The  ladybird^ 
or  ladybng,  lives  almost  entirely 
upon  aphids  and  scale  insects, 
both  in  the  larval  and  the  mature 
state,  and  is  one  of  the  most  effec- 
tive aids  we  have  in  keeping  these 
pests  in  check.  Most  remarkable 
of  all,  however,  are  the  ichneumon 
fiies  which  deposit  their  eggs  in 
the  larvcB  of  other  insects.  Some 
are  equipped  with  long  oviposi- 
toi-s,  by  means  of  which  they  are 
able  to  reach  the  larvse  of  boring  species,  deep  in  the  trunks 
of  trees.    When  the  eggs  hatch,  the  young  worms  live  upon 


Fig.  186.   One  of  the  larger  ich- 
neumon flies.  (About  natural  size) 


INSECT  PESTS  257 

the  tissues  of  their  host,  instinctively  avoiding  the  vital  parts 
until,  having  reached  maturity,  they  eat  their  way  out  to  the 
air  and  spin  their  small  cocoons  upon  the  body  of  their  host. 
Soon  the  perfect  insect  emerges  and  flies  away  to  look  for  new 
victims,  leaving  the  parasitized  host  to  die.  The  tomato  worm 
is  very  frequently  parasitized,  and  a  search  in  any  large  tomato 
patch  late  in  summer  will  probably  reveal  many  worms  cov- 
ered with  the  tiny  white  cocoons  of  the  parasite. 

PRACTICAL  EXERCISES 

1.  Make  a  list  of  the  insects  injurious  to  plants  in  your  locality, 
showing  what  crops  they  injure.  Underscore  the  chewing  insects  in 
the  list. 

2.  Place  a  cross  before  the  names  of  insects  in  the  preceding  list 
that  liave  been  found  in  the  school  garden. 

3.  Make  a  list  of  the  five  most  destructive  insects  in  your  locality  and 
indicate  whether  it  is  the  larvse  or  perfect  insect  that  does  the  damage. 

4.  Make  a  collecting  trip  for  insects,  securing,  if  possible,  eggs, 
larvae,  pupae,  and  perfect  insects  of  the  same  species.  This  may  be  pos- 
sible with  the  cabbage  worm  and  a  few  others.  Catch  young  crickets 
or  grasshoppers  and  compare  with  mature  forms. 

5.  Search  tomato  vines  for  parasitized  tomato  worms.  Similarly, 
parasitized  worms  may  be  found  on  grapevines,  the  box  elder,  the  apple, 
and  many  others. 

6.  Collect  and  label  samples  of  all  of  the  poisons  used  for  combat- 
ing insects. 

7.  Examine  collections  of  insects  for  the  dragon  flies,  ladybug.s, 
ichneumon  flies,  ant  lions,  and  other  insects  that  prey  upon  harmful 
species. 

References 

Bailey,  "Manual  of  Gardening." 
Fernow,  "Care  of  Trees." 

Farmer^  Bulletins 

99.  Insects  Injurious  to  Shade  Trees. 
127.  Important  Insecticides. 
146.  Insecticides  and  Fungicides. 
155.  How  Insects  affect  the  Health  in  Rural  Districts. 
196,  Usefulness  of  the  Common  Toad. 


CHAPTER  XVIII 


PLANT   BREEDING 


Need  for  breeding.  It  is  well  known  that  fruits  and  flowers 
as  they  grow  in  the  wild  rarely  attain  the  perfection  of  which 
they  are  capable  under  more  favorable  circumstances.  The 
struggle  for  sufficient  light  and  food  materials,  the  constant 
conflict  with  insects  and  disease,  and  the  vicissitudes  to  which 
the  plants  are  exposed  by  the  climate  of  the  region  all  operate 
to  reduce  that  vitality  which  otherv\nse  might  be  expended  in 


Photograph  by  U.  L.  UoUiBter  Laud  Co. 

Fig.  187.    Four  potatoes  to  the  yard 
These  are  the  result  of  irrigation  farming 

brighter  flowers  and  larger,  better-flavored,  and  more  abundant 
fruits.  All  cultivation  is  in  recognition  of  this  fact ;  reduced 
to  its  simplest  terms,  it  is  the  selection  of  the  most  likely 
plants,  the  supplying  them  with  abundant  food,  and  the  pro- 
tecting of  them  from  their  enemies.  Cultivation  always  results 
in  better  and  larger  crops,  but  man  has  not  been  content  to 
rest  here.  Having  been  taught  by  this  experience  that  plants 
can  be  greatly  modified  by  proper  treatment,  he  is  ever  on  the 
watch  to  extend  his  operations  further  and  produce  still  better 

258 


PLANT  BREEDING 


259 


specimens.  This  work  of  improving  plants  by  inducing  them 
to  attain  the  highest  development  possible  is  called  plant 
breeding. 

Basis  for  breeding.  The  work  of  plant  breeding  is  made 
possible  by  the  fact  that  all  plants  tend  to  vary  within  certain 
limits.  There  is  probably  no  species  that  is  absolutely  fixed  as 
to  type,  though  some  vary  more  than  others.  Even  in  the 
plants  which  present  the  least  amount  of  variation,  nobody 
ever  saw  two  plants  or  even  two  leaves  that  were  exactly 
alike.  Usually  the  plants  that  vary  most 
come  from  families  that  contain  great  num- 
bers of  species ;  in  fact,  the  species  them- 
selves may  be  looked  upon  as  illustrations 
of  greater  variations  from  the  original  stock 
which  have  been  developed  through  ages  of 
natural  selection.  Every  one  is  so  familiar 
with  the  slight  variations  that  occur  in  all 
plants  that  they  seldom  occasion  remark. 
In  any  large  area  devoted  to  a  single  species 
we  expect  to  find  the  tall  and  the  short,  the 
brand  led  and  the  unbranched,  the  smooth 
and  the  hairy,  the  pale  and  the  more  deeply 
colored,  the  vigorous  and  the  sickly,  the 
drought-resistant  and  the  less  hardy.  It  is 
only  when  variation  is  manifested  in  the  plant  parts  with  which 
we  are  especially  concerned,  such  as  the  size  and  color  of  the 
flowers  or  the  abundance,  size,  and  flavor  of  the  fruits,  that 
we  notice  it  and  endeavor  to  make  these  favorable  variations 
permanent.  That  they  can  be  made  permanent,  or  even  in- 
creased in  value,  is  shown  by  the  superior  plants  everywhere 
seen  in  cultivation.  Strongly  marked  variations  are  usually 
apparent  in  the  seedlings  soon  after  they  have  started  into 
growth,  but  others  may  not  appear  until  the  species  has 
reached  maturity.    The  point  of  departure  for  most  plant 


Fig.  188.  A  geva- 
iiiuin  sport,  show- 
ing one  truss  of 
flowei's  growing  out 
of  anotlier 


260 


AGRONOMY 


breeding  is  found  in  the  seeds,  however.  By  repeated  sow- 
ings of  great  numbers  of  seeds  one  will  ultimately  secure  the 
material  necessary  for  a  start  and  can  then  breed  from  it. 

The  common  cut-leaved  maple 
Avas  not  found  until  a  million 
maple  seeds  had  been  sown, 
and  it  is  said  that  a  bushel 
of  apple  seeds  were  sown 
before  that  desirable  form,  the 
wealthy  apple,  was  secured. 
The  weeping  mulberry  was  an 
accidental  seedling  that  sprung 
into  being  fully  developed,  and 
the  Lombardy  poplar  is  re- 
garded as  a  sport  from  the  Eu- 
ropean black  poplar.  In  the 
more  permanent  plants,  such 
as  shrubs  and  trees,  variations 
occur  which  are  often  confined 
to  a  single  branch  or  a  single  cluster  of  flowers.  These  are 
called  bud  variations.  Good  illustrations  may 
be  found  in  the  nectarine,  which  is  regarded 
as  a  bud  variation  of  the  peach,  and  in  the 
seedless  navel  orange,  which  has  been  derived 
in  the  same  way  from  the  seeded  orange.  It 
is  probable  that  variations  from  the  normal 
are  much  more  frequent  in  nature  than  we 
suspect,  and  the  fact  that  they  seldom  persist 
is  no  proof  that  they  do  not  occur.  In  the 
nature  of  things  the  plants  of  a  region  are 
better  adapted  to  that  region  than  any  other 
set  would  be,  and  are  thus  able  to  hold  the  ground  and  crowd 
out  any  different  forms  that  might  arise.  If,  as  may  occasion- 
ally happen,  the  new  form  is  better  fitted  to  the  locality  than 


Fig.  189.   A  nasturtium  sport,  show- 
ing tlie  parts  of  tlie  flower  turned 
to  leaves 


Fig.  100.  Colum- 
bine flower  with 
parts    turned   to 
leaves 


PLANT  BREEDING  261 

the  normal  plants,  it  may  take  jjossession  of  the  field  and  ex- 
clude the  others.  Wlien  a  variation  in  a  plant  makes  it  very 
different  from  the  original,  it  is  commonly  known  as  a  sport, 
or  mutation.  Thus  a  red-flowered  form  may  suddenly  appear 
among  plants  that  normally  bear  white  or  yellow  flowers, 
double  flowers  may  spring  up  in  the  midst  of  single-flowered 
specimens,  or  well-flavored  fruits  may  be  discovered  among 
inferior  kinds.  The  Lucretia  dewberry  was  derived  from  the 
wild  dewberry  in  this  way,  and  many  of  our  bush  fruits  have 
had  a  similar  origin.  The  Concord  grape  is  another  interest- 
ing example  of  a  sport  derived  from  a  familiar  wild  plant. 

Inducing  variation.  While  one  may  occasionally  find  among 
wild  plants  a  desirable  specimen  that  has  arisen  from  seed  or 
bud  variation,  and  transplant  it  to  better  quarters  before  the 
common  plants  of  the  region  have  overwhelmed  it,  the  task  of 
watchmg  either  wild  or  cultivated  plants  until  such  variations 
occur  is  a  tedious  one.  Fortunately  for  the  plant  breeder,  it 
has  been  found  possible  to  hasten  matters  and  to  induce  vari- 
ation by  manipulating  the  plants  in  various  ways.  Increasing 
the  food  supply  is  one  of  the  most  efficient  means  of  produc- 
ing variation.  It  seems  as  if  many  qualities  latent  in  the  plant 
are  only  brought  out  when  food  is  abundant  and  all  the  other 
conditions  for  growth  are  favorable.  A  change  in  location  may 
also  cause  plants  to  vary.  When  they  have  grown  for  any 
length  of  time  in  one  region,  they  become  in  a  measure  spe- 
cially adapted  to  it  and  have  little  further  need  of  change ; 
removal  to  a  different  region  calls  for  new  adjustments,  and 
consequently  favors  variation.  Farmers  and  gardeners  often 
send  to  other  localities  for  a  change  of  seed,  and  it  is  believed 
that  the  practice  of  buying  new  seeds  from  the  seedsmen  each 
year,  instead  of  saving  seeds  from  the  previous  crop,  may 
affect  the  character  and  variability  of  the  new  plants  grown. 
A  difference  in  the  amount  of  light  received  by  the  plant  is 
still  another  cause  of  variation.    Pruning  has  a  similar  effect, 


262 


AGRONOMY 


partly  through  admitting  more  light  to  the  plant,  and  partly 
through  checking  growth  processes.  Injury  to  the  plant  may 
also  result  in  variation.  It  is  a  remarkable  fact  that  when  the 
type  has  once  been  induced  to  "  break,"  or  vary,  the  tendency 
for  the  resulting  forms  to  continue  to  do  so  is  strong.    A 

notable  instance  is 
found  in  the  plant 
known  as  the  Boston 
feni,  which  is  fre- 
quently grown  in  the 
window  garden.  A 
few  years  ago  a  sport 
with  much-divided 
leaves  was  put  on 
the  market,  but  it 
was  soon  eclipsed  by 
numerous  much  finer 
forms  that  had  been 
developed  from  it. 
When  once  a  desira- 
ble variation  has  been 
secured,  its  value 
need  not  be  jeop- 
ardized by  further 
breeding.  It  may 
then  be  multiplied 
vegetatively ;  in  fact,  many  improved  plants  will  not  come 
true  from  seeds,  and  their  number  must  be  increased  in  this 
way.  Most  of  our  fruits,  flowers,  and  garden  vegetables  have 
arisen  through  variations  from  less  desirable  types. 

Hybrids  and  hybridizing.  Another  way  in  which  new  plants 
may  be  obtained  or  variations  started  is  by  crossing,  or  hybridiz- 
ing. In  this  process  pollen  from  the  flowers  of  one  species,  or 
variety,  is  applied  to  the  stigmas  in  the  flowers  of  another. 


Fig, 


Photograph  by  W.  A.  Terry 

191.    Two  leaf  sports  from  the  comuion 
Christmas  fern  (Polyntichum) 


PLANT  BREEDING  263 

the  resulting  seeds  thus  havmg  the  characteristics  of  two  dif- 
ferent strains.  The  plants  from  such  seeds  are  called  crosses^ 
or  hyhrids.  A  few  hybrids  between  different  genera  are  known, 
but  usually  only  closely  related  species,  or  varieties,  are  likely 
to  cross,  and  the  closer  the  relationship  the  more  successful 
the  operation  is  likely  to  be.  The  apple  will  not  hybridize 
with  the  pine,  nor  the  strawberry  with  the  milkweed.  The 
reason  species  do  not  cross  more  readily  is  because  the  tendency 
in  nature  is  away  from  such  crossing.  If  it  were  otherwise,  we 
would  have  an  endless  confusion  of  plant  forms  in  which  no 
type  would  be  recognizable.  Among  the  more  interesting  forms 
of  commercial  value  that  have  been  produced  by  hybridizing 
are  the  plumcot,  a  hybrid  between  the  plum  and  apricot;  the 
citrange,  a  hybrid  between  the  trifoliate  orange,  or  citron,  and 
the  sweet  orange ;  and  the  tangelo,  produced  by  crossing  the 
tangerine  orange  and  the  grapefruit  (pomelo).  Among  plants 
cultivated  for  their  flowers,  the  canna,  gladiolus,  and  orchid 
have  been  extensively  hybridized. 

Producing  the  cross.  In  crossing  plants  the  essential  thing 
is  to  protect  from  all  foreign  pollen  the  stigmas  of  the  flowers 
to  be  pollinated.  This  is  accomplished  by  slipping  a  small 
paper  bag  over  the  flowers  just  before  they  open,  and  tying 
the  open  end  of  the  bag  about  the  twig  which  bears  them.  If 
one  is  to  be  absolutely  sure  of  his  cross,  the  flowers  that  are 
to  supply  the  pollen  should  be  similarly  treated.  If  the  flowers 
contam  both  carpels  and  stamens,  as  is  usually  the  case,  there 
is  a  chance  that  the  flowers  to  be  crossed  may  be  pollinated 
by  their  own  stamens  unless  these  are  removed.  It  is  custom- 
ary, therefore,  to  cut  away  the  corolla  with  a  sharp  pair  of 
scissors  before  the  flower  expands,  and  remove  the  stamens 
with  small  forceps  or  the  scissors.  In  plants  like  the  pump- 
kin, cucumber,  and  corn,  which  bear  their  stamens  and  carpels 
in  separate  flowers,  this  treatment  is  not  required,  though  the 
flowers  should  be  protected  from  the  wind,  insects,  and  other 


264  AGRONOMY 

pollinating  agencies.  In  pollinating  the  flower  the  ii|)e  anther 
is  crushed  to  expose  the  pollen,  which  is  then  thickly  applied 
to  the  waiting   stigmas.     Fresh  pollen   is  always  best,  but 

in  a  few  cases,  especially  in 
orchids,  it  may  remain  alive 
for  months.  After  pollination 
the  flower  is  once  more  cov- 
ered with  the  paper  .  bag 
until  the  stigma  is  no  longer 
receptive  and  the  ovary  has 
begun  to  increase  in  size.  In 
Fig.  1j>2.  Lungitudinal  section  of  all  plants  that  bear  both  kinds 
flower    and    another    prepared    for        ^  .      .,  „ 

jjj    tj  or  organs  m  the  same  nower 

two  crosses  can  be  made,  the 
stamens  of  one  plant  supplying  pollen  for  the  other,  and 
vice  versa.  Sometimes  a  considerable  difference  exists  in  the 
progeny  of  the  two  crosses,  though  usually  there  is  practi- 
cally none. 

Mendel's  law.  About  half  a  century  ago  an  Austrian  monk 
named  Gregory  ISIendel,  while  experimenting  with  different 
strains  of  peas  in  the  monastery  garden,  discovered  the  curious 
law  that  governs  the  union  of  male  and  female  elements  by 
which  hybrids  are  produced.  An  account  of  his  experiments 
was  published  at  the  time,  but  the  significance  of  the  results 
did  not  impress  the  botanists  of  his  day,  and  it  was  not  until 
1900,  when  the  law  was  again  independently  discovered,  that 
the  importance  of  Mendel's  work  was  recognized  and  the  origi- 
nal experimenter  given  proper  credit.  Briefly  the  law  is  this : 
when  two  species,  or  forms,  are  crossed,  the  resulting  hybrids 
tend  to  resemble  one  parent  to  the  exclusion  of  the  other. 
Thus  if  a  red-flowered  and  a  white-flowered  form  be  crossed, 
the  next  generation  is  likely  to  have  all  red  or  all  white 
flowers.  If  the  flowers  are  red,  we  say  the  red  color  is  dominant 
and  the  white  recessive;  or  if  the  flowers  are  white,  the  red  is 


PLANT  BREEDING 


265 


recessive  and  the  white  dominant.  That  the  color  said  to  be 
recessive  is  merely  latent  and  not  lost  is  shown  when  the  next 
generation  of  plants  is  produced.  Here  the  recessive  color 
appears  again  in  approximately  one  quarter  of  the  specimens ; 
and  if  these  recessive  plants  are  now  bred  together  for  gener- 
ations, they  will  bring  no  plants  of  the  other  color.  Quite  a 
different  state  of  affairs  exists  in  the  behavior  of  the  remain- 
ing three  quarters  of  the  specimens.  If  the  recessive  color 
is  white,  then  these 
latter  will  be  red,  but 
only  about  one  thbd 
of  them,  that  is,  one 
quarter  of  the  whole 
number  of  plants, 
will  be  capable  of 
producing  only  red 
flowers  in  the  next 
generation,  and  so  on 
indefinitely.  The  re- 
maining 50  per  cent 
of  the  original  num- 
ber will  produce  as 
before,  approximately 
one  quarter  pure  red, 
one  quarter  pure  white,  and  one  half  mixed,  and  this  con- 
dition will  continue  through  many  successive  generations.  In 
explanation  of  this  it  is  assumed  that  in  the  original  white- 
flowered  species  all  the  gametes,  or  sexual  cells,  of  the  plant 
had  the  tendency  to  produce  other  white-flowered  forms,  and 
the  equivalent  cells  in  the  red-flowered  plants  had  a  tendency 
to  produce  red  flowers.  When  they  are  bred  together,  there- 
fore, the  resulting  plants  are  bound  to  have  a  mixture  of  red 
and  white  gametes,  one  of  which  becomes  dominant  in  this 
second  generation.    In  the  next  generation,  however,  the  male 


Fig.  193.  Diagram  to  illu.sti*ate  Mendel's  law 


266  AGRONOMY 

and  female  gametes  have  another  chance  to  pair,  and  this 
naturally  results  in  some  plants  being  produced  from  the 
pairing  of  two  white  gametes,  and  others  from  two  rejl  ones, 
while  still  others  continue  to  be  mixed  as  before.  The  example 
cited  is  probably  much  simpler  than  is  usually  the  case  in 
nature  when  a  cross  is  made,  since  it  is  concerned  with  a 
single  character  only.  It  is  likely  that  a  similar  relationship 
exists  between  each  pair  of  contrasting  characters  in  the  plants 
hybridized,  one  character  being  dominant  and  one  recessive  in 
the  first  generation,  but  both  appearing  in  the  second  in  the 
proportions  indicated.  Smooth  leaves  may  be  recessive  to 
downy  ones,  short  stems  may  be  dominant  over  long  ones, 
large  flowers  dominant  over  small  ones  or  the  reverse.  Thus 
the  skillful  cultivator  is  presented  the  opportunity  of  varying 
his  plants  in  many  ways  by  combining  the  characters  differ- 
ently. It  must  not  be  assumed,  however,  that  all  plants  be- 
have in  the  manner  outlined  in  the  foregoing.  There  are  some 
crosses  which  are  more  or  less  perfect  blends  of  the  original 
forms,  and  others  in  which  the  characters  do  not  appear  to 
separate  out  according  to  Mendel's  law  in  the  succeeding  gen- 
eration. In  others  certain  characters  may  blend,  though  the 
species  as  a  whole  behaves  according  to  the  law.  What  these 
characters  are  and  how  they  function  in  crossing  is  still  a  sub- 
ject for  investigation.  Crossing  two  forms  in  which  some  of 
the  characters  are  alike  may  also  result  in  intensifying  these 
characters. 

Selection.  Variations  of  whatever  kind  merely  offer  oppor- 
tunities for  plant  breeding;  they  give  different  plants,  not 
necessarily  better  ones.  The  new  forms  are  possibly  as  fre- 
quently below  a  desired  standard  as  above  it.  Any  permanent 
improvement  must  be  made  by  careful  and  wise  selection. 
The  gardener  practices  a  certain  form  of  plant  breeding, 
though  possibly  unconsciously,  when  he  selects  seeds  from  his 
best  plants  for  producing  the  next  year's  crops.    To  achieve 


PLANT  BREEDING 


267 


any  noteworthy  success,  however,  the  plant  breeder  must  have 
an  ideal  type  clearly  in  mind  and  breed  toward  it.  No  progress 
will  be  made  if  the  ideals  are  constantly  changing  and  the 
plants  selected  for  one  feature  one  year,  and  another  feature 
the  next.  By  keeping  the  desired  form  constantly  in  view, 
taking  advantage  of  all  favorable  variation  and  always  select- 
ing the  best,  a  steady  advance  may  be  made  for  a  series  of 
years.  Now  and  then  a  sport  may  develop  which  will  suddenly 
carry  the  work  forward  with  a  bound,  but  usually  the  small 
variations  must  be  depended  upon.   There  is  a  point,  however, 


Photosrapli  from  Bergen  and  Caldwell's  "Practical  Botany" 

Fig.  194.   A  prize  ear  of  corn  that  sold  for  two  hundred  fifty  dollars 

beyond  which  each  plant  refuses  to  go.  It  would  probably 
be  impossible  to  produce  tomatoes  as  large  as  pumpkins, 
though  the  size  might  be  greatly  increased  by  selection  and, 
in  fact,  has  been.  Nor  is  it  likely  that  a  blue-flowered  form 
could  be  developed  from  one  with  red  flowers,  though  the  color 
in  the  blue  flowers  might  be  varied  greatly  by  such  means. 
The  average  amount  of  sugar  in  sugar  beets  has  been  raised 
from  8  per  cent  to  18  per  cent  within  a  very  short  time, 
while  single  specimens  have  been  found  with  much  higher 
sugar  content.  In  plant  breeding  it  is  usual  to  pay  more 
attention  to  the  average  advance  than  to  single  cases,  since 


268  AGRONOMY 

widely  aberrant  forms  are  seldom  stable.  It  is  better  to  breed 
from  a  jjlant,  all  of  whose  members  show  some  advance  along 
the  lines  desired,  than  to  breed  from  one  which  shows  a 
greater  advance  in  a  single  member.  In  breeding  for  large 
flowers,  for  instance,  one  should  select  plants  in  which  all  the 
flowers  are  a  little  larger,  rather  than  a  small-flowered  form 
which  may  produce  one  or  two  superior  blossoms.  It  is  also 
desirable  to  breed  for  one  thing  at  a  time,  or,  if  more  is 
attempted,  to  choose  characters  which  will  not  conflict  in 
developing. 

Roguing.  After  a  form  has  been  developed  to  a  point 
where  its  superiority  to  the  common  form  is  apparent,  it  can- 
not be  depended  upon  to  continue  in  this  state  without  assist- 
ance. Left  to  itself  it  will  soon  "  run  out,"  that  is,  it  will  return 
to  the  general  average  of  the  type,  and  the  improvement  gained 
by  breeding  be  lost.  When  the  plants  have  acquired  the  de- 
sired form,  further  variation  is  undesirable  and  effort  must 
now  be  directed  to  fixing  the  type.  All  plants,  therefore,  that 
are  not  close  to  the  ideal  form  should  be  destroyed  as  soon  as 
detected,  to  prevent  the  good  and  bad  plants  from  mixing  by 
pollination.  This  is  called  roguing.  If  one  is  endeavoring  to 
breed  a  certain  strain  of  plants,  he  will  sow  as  many  seeds  as 
possible,  preserve  only  the  best  for  subsequent  breeding,  and 
destroy  the  others. 

Xenia.  When  a  cross  between  two  plants  is  made,  any  dif- 
ferences due  to  the  union  will  not  appear  until  a  new  genera- 
tion has  been  grown  from  the  seeds  resulting  from  the  cross. 
In  certain  cases,  however,  the  seeds  themselves,  or  even  the 
fruit,  may  show  the  effects  of  crossing.  A  good  illustration 
may  be  had  in  corn,  which  readily  mixes  when  two  sorts  are 
grown  together.  This  effect  is  known  as  xenia.  Ordinarily, 
when  a  plant  is  fertilized,  a  single  gamete  from  the  pollen  tube 
unites  with  another  in  the  ovule  to  form  the  cell  from  which 
the  embryo  is  produced.    In  cases  of  xenia  another  gamete 


PLANT  BREEDING  269 

from  the  pollen  tube  unites  with  the  nucleus  of  the  cell 
in  which  the  female,  or  egg,  cell  is  located,  and  this,  though 
unable  to  form  an  embryo,  may  nevertheless  grow  and  form 
part  or  all  of  the  endosperm,  or  albumen,  which  usually  sur- , 
rounds  the  embryo  in  the  seeds.  In  the  corn,  xenia  affects 
only  the  endosperm,  though  the  fact  that  the  second  union 
of  cells  has  been  made  is  proof  that  the  embryo  in  such 
seeds  has  also  been  produced  from  the  sexual  cells  of  two 
different  strains. 

Parthenogenesis.  While  it  is  the  rule  that  neither  seeds  nor 
young  plants  result  from  flowers  unless  fertilization  takes  place, 
there  are  not  a  few  species  that  are  able  to  produce  new  embryos 
without  this  process.  The  production  of  young  plants  in  this 
way,  from  what  are  essentially  unfertilized  eggs,  is  called  par- 
thenogenesis. This  phenomenon  is  not  entirely  confined  to  plant 
life.  The  aphids,  or  plant  lice,  reproduce  by  parthenogenesis, 
and  there  are  sometimes  as  many  as  thirteen  generations  of 
parthenogenetically  produced  females  before  a  generation  con- 
taining males  is  produced.  Parthenogenesis  differs  from  ordi- 
nary vegetative  reproduction  in  plants  in  that  it  always  results 
from  an  egg  cell,  while  in  vegetative  reproduction  any  part  of 
the  plant  may  give  rise  to  a  new  plant. 

PRACTICAL  EXERCISES 

1.  Find  the  amount  of  variation  that  is  exhibited  by  a  hundred 
specimens  of  one  kind  selected  at  random,  counting  or  measuring  the 
parts  as  necessary.  The  following  list  is  suggestive :  pods  of  catalpa 
(variation  in  length  and  diameter) ;  peas  or  beans  (number  in  pod) ; 
sepals  (colored  organs)  in  hepatica  (variations  in  number ;  in  color)  ; 
petals  of  bloodroot  (number)  ;  ray  flowers  of  daisy,  sunflower,  or  other 
composite  (number);  lobes  of  the  leaves  in  mulberry  (number)  ;  leaves 
in  poplar  or  apple  (width  and  breadth)  ;  leaflets  in  mountain  ash,  locust, 
or  rose  (number)  ;  fruits  in  a  cluster  of  currants  or  grapes  (number). 
In  counting  or  measuring  make  a  column  of  figures  in  numerical  order, 
and  opposite  each  figure  make  a  straight  mark  each  time  a  count  falls 
upon  it.    Every  fifth  mark  is  made  across  the  preceding  four,  so  that  the 


270  AGRONOMY 

marks  may  be  counted  by  fives.  In  the  illustration  which  represents 
the  variation  in  the  ray  flowers  of  55  specimens  of  sunflower  the  lowest 
number  of  rays  found  was  12,  and  five  speci- 
mens possessed  this  number.  The  highest 
•  number  was  20  with  only  one  plant  show- 
ing it.  The  average  was  15,  twelve  heads 
possessing  this  number.  The  same  data 
can  be  expressed  by  a  graph,  similar  to 
the  one  on  page  52,  in  which  the  squares 
may  represent  the  number  of  parts  in  one 
direction  and  the  number  of  specimens 
in  the  other.  Express  your  work  by  both 
methods. 

2.  Visit  any  considerable  area  of  one 
crop,  wild  or  cultivated,  and  select  the  speci- 
mens you  would  breed  from  if  you  desired 
to  get  (rt)  larger  flowers,  (/>)  more  vigorous 
plants,  (c)  deeper  color,  (J)  more  abundant 
fruit,  or  (e)  broader  leaves. 

3.  Visit  any  patch  of  flowers  in  full 
bloom  and  search  for  variations  in  color, 
size,  and  number  of  parts  in  the  flower. 

4.  In  a  row  of  young  seedlings  select   p,^_  ^q;^    Variation  iu  the 
those  that  are  (a)  most  vigorous,  (b)  weak-      j-ay  flowers  of  sunflower 
est,  (c)  deepest  in  color,  (r7)  palest,  (e)  with 

broadest  leaves,  and  (/)  with  narrowest  leaves.    Are  the  differences 
great  enough  to  be  readily  noticeable?   Would  they  affect  the  crop? 

5.  Visit  and  examine  any  sport  that  may  be  growing  in  the  neigh- 
borhood, especially  the  cuWeaved  maple,  Camperdown  elm,  weeping 
mulberry,  single-leaved  mountain  ash,  single-leaved  locust,  iiectarine, 
purple-leaved  plum,  purple-leaved  barberry,  golden  elder,  yellow  rasp- 
berry, and  the  like.    Compare  with  normal  plants. 

6.  In  the  school  garden  or  other  convenient  place  cross-pollinate 
one  or  more  flowers.  Make  a  reciprocal  cross  in  others.  If  two  desirable 
varieties  are  crossed,  save  the  seeds  for  the  next  class  to  use. 

7.  Plant  hemp  seed  and  study  the  difference  between  the  male 
(staminate)  and  the  female  (pistillate)  plants.  Examine  cucumber  or 
melon  plants  and  distinguish  pistillate  and  staminate  blossoms. 

8.  If  seeds  of  hybrid  plants  are  to  be  obtained  (perhaps  left 
by  a  previous  class),  grow  the  plants  to  observe  the  workings  of 
Mendel's  law. 


/o 

II 

12 

ruj 

13 

tnj  1 

Hi- 

mj  III 

15 

iw  mi  II 

16 

IW  IW 

17 

MJ  II 

18 

IW 

19 

II 

20 

1 

PLANT  BREEDING  271 

9.  Pick  out  two  antagonistic  strains  in  some  garden  plant,  such  as 
tall  and  short,  broad-leaved  and  narrow-leaved,  large  flowers  and  small, 
and  by  selection  breed  up  two  different  races.  Leave  the  seeds  for  the 
next  class  to  use  in  continuing  the  exj)eriment.  Be  sure  to  make  a  full 
record  of  your  work  for  future  reference. 

10.    Examine  ears  of  corn  that  have  mixed  for  illustrations  of  xenia. 
Cross-pollinate  corn  of  two  different  colors  and  observe  the  effects. 

References 

Bailey,  "Plant  Breeding." 

Davenport,  "Domesticated  Animals  and  Plants." 

Davenport,  "Principles  of  Breeding." 

De  Vries,  "Plant  Breeding." 

Farmers^  Bulletin 

334.  Plant  Breeding  on  the  Farm. 

Bureau  of  Plant  Industry 

16.5.  The  Application  of  the  Principles  of  Heredity  to  Plant  Breeding. 
1()7.  New  Methods  of  Plant  Breeding. 


CHAPTER  XIX 

THE  ORIGIN  OF  SPECIES 

Evolution.  Everything  in  nature  is  subject  to  change.  No 
sooner  is  a  form  produced  or  a  structure  completed  than  it 
begins  to  be  modified  by  man.y  agencies.  Ultimately  it  grows 
old,  slowly  deteriorates,  and  finally  disappears.  Such  changes 
have  always  been  in  existence.  We  know  from  the  fossil  ani- 
mals and  plants  found  in  the  rocks  that  there  has  been  a  steady 
succession  of  different  forms  in  the  world,  beginning  with  the 
strange  and  incongruous  forms  of  past  ages  and  ending  with 
the  species  of  the  present  day.  The  fact  that  such  forms  are 
embedded  in  the  solid  rock  shows  that  the  very  rocks  them- 
selves have  changed  since  animals  and  plants  first  inhabited 
the  earth,  and  also  indicates  how  very  profoundly  our  planet 
has  been  modified  since  time  began.  When  we  realize  that 
the  one  unchangmg  feature  of  existence  is  change,  it  is  easy 
to  appreciate  the  fact  that  the  plants  and  animals  of  our  day 
are  quite  unlike  those  that  first  inhabited  the  earth.  All  have 
changed  with  changing  conditions  ;  indeed,  within  the  memory 
of  living  men  some  of  our  flowers  and  fruits  have  been  greatly 
modified  in  this  way.  Our  present  species,  then,  appear  to  be 
the  latest  forms  in  a  long  line  of  descent  —  the  last  links  in  a 
chain  that  might  be  traced  back  to  the  dawn  of  creation.  The 
process  by  which  our  modern  plants  have  come  to  be  what 
they  are,  the  steps  by  which  they  have  changed,  little  by  little, 
are  included  in  the  term  "  evolution."  It  is  usual  to  assume  that 
evolution  has  always  progressed  from  the  simple  to  the  com- 
plex, and  so  it  has  in  most  cases ;  but  evolution  may  proceed 
in  any  direction  useful  to  the  organism,  and  the  best  we  can 
say  of  it  is  that  it  works  through  change. 

272 


THE  ORIGm  OF  SPECIES  273 

Struggle  for  existence.  Every  plant  is  able  to  ripen  many 
more  seeds  than  are  needed  to  reproduce  the  original  specimen. 
In  some  annuals  nearly  a  million  seeds  may  be  produced,  and 
the  perennials  often  do  as  well  and  contmue  to  do  so  for  many 
years  in  succession.  But  the  earth  is  already  so  densely  pop- 
ulated that  there  is  no  chance  for  all  the  plants  from  these 
seeds  to  come  to  maturity,  even  if  they  escape  the  multitude 
of  dangers  that  attend  them  on  every  side.  Many  of  the  seeds 
fall  in  places  where  germination  is  impossible,  —  on  rocks,  in 
roads  and  streets,  in  streams  and  ponds,  —  and  others  are  eaten 
by  birds,  insects,  and  other  animals.  Those  that  germinate  are 
subject  to  plant  diseases  and  the  attacks  of  insects,  late  frosts 
may  cut  them  down,  the  hot  sun  may  bum  them  up,  and 
drought  may  cause  their  death.  Many  spring  up  in  the  shade 
of  other  plants  or  in  uncongenial  soil  and  die  for  want  of  food, 
while  the  crowd  of  other  plants  seeking  the  same  advantages 
with  regard  to  light  and  food  materials  is  so  great  that  only 
the  exceptional  individual  is  able  to  survive.  Thus  there  is  a 
very  real  and  constant  struggle  going  on,  a  struggle  of  species 
with  species,  of  individual  with  individual,  and  all  with  the 
untoward  forces  of  nature.  As  applied  to  plants  and  animals 
this  is  called  the  struggle  for  existence,  and  it  results  in  the 
survival  of  the  fittest.  Here  we  discover  one  reason  for  the 
numerous  seeds  produced  by  plants.  The  greater  the  n-umber 
produced,  the  greater  the  chance  that  at  least  a  few  will 
survive  to  replace  the  original  form. 

Natural  selection.  The  plants  that  survive  all  the  vicissi- 
tudes of  nature  and  finally  come  to  maturity  are,  as  we  have 
seen,  those  that  in  the  long  run  are  best  fitted  to  survive.  A 
slightly  larger  amount  of  food  in  the  seed  may  have  given 
them  a  start  over  weaker  plants  in  the  vicinity,  a  more  rapidly 
growing  root  may  have  brought  them  into  contact  with  mois- 
ture sooner,  the  ability  to  get  along  with  less  light  may  have 
enabled  them  to  survive,  or  any  one  of  a  hundred  other  things 


274  AGRONOMY 

may  have  given  them  some  advantage  over  their  competitors 
and  helped  them  to  hold  their  lead  in  the  race.  Those  less 
able  to  carry  on  the  struggle  ultimately  and  inevitably  perish. 
Thus  there  is  in  nature  a  constant  and  widespread  selection 
of  the  best,  quite  akin  to  that  which  man  exercises,  with  this 
difference,  that  in  natural  selection  the  plants  are  steadily 
adapted  to  their  habitats  and  the  species  and  varieties  kept  up 
to  standard ;  while  in  artificial  selection,  such  as  man  prac- 
tices, the  aim  has  been  to  produce  better  strains  for  certain 
purposes  without  regard  to  the  ability  of  the  plant  to  survive 
in  the  struggle  with  other  plants,  smce  cultivation  relieves  the 
plant  of  much  of  this  struggle.  This  explains  why  our  garden 
plants  are  so  easily  overcome  by  weeds.  They  have  been  cul- 
tivated so  long,  that  they  have  lost  the  power  to  take  care  of 
themselves.  The  weeds,  on  the  other  hand,  have  been  de- 
veloped into  most  efficient  plants  both  by  nature  and  by  the 
hand  of  the  gardener.  Only  the  most  resistant  could  withstand 
the  two. 

Results  of  variation.  Without  variation  evolution  would 
be  at  a  standstill  and  no  possibility  of  improvement  would 
exist.  The  tendency  of  plants  to  constantly  vary  in  different 
directions  has  saved  whole  races  from  extinction,  while  the  in- 
ability to  change  with  changing  conditions  has  as  certainly 
caused  the  death  of  many  others.  Plants  are  never  perfectly 
adapted  to  their  habitats,  but  variation  enables  them  to  fit 
into  the  plant  covering  of  the  region  with  the  least  friction, 
while  nature  constantly  weeds  out  the  unfit.  Usually  the 
changes  in  plants  are  cumulative,  and,  given  sufficient  time, 
two  plants  nearly  alike  at  the  beginning  may  ultimately  come 
to  be  very  different  if  exposed  to  different  conditions.  It  is 
not  difficult  to  see  that  all  the  plants  which  now  inhabit  the 
earth  may  have  been  derived  from  a  single  primitive  form 
through  long  ages  of  variation.  This  explains  the  existence 
of  many  plants  of  the  same  general  type  —  they  have  been 


THE  ORIGIN  OF  SPECIES  275 

derived  from  a  common  ancestor  in  the  not  far  distant  past. 
In  the  case  of  plants  that  less  closely  resemble  one  another,  it 
is  conceivable  that  the  common  ancestor  has  existed  farther 
back  in  the  line  of  descent. 

Darwinian  theory.  Ever  since  man  began  to  think  about 
plants  he  has  speculated  more  or  less  as  to  their  origin.  Al- 
though the  great  mass  of  people  have  always  believed  that 
plants  have  existed  unchanged  from  the  beginning,  there  have 
been  people  in  every  age  to  point  out  evidences  of  change, 
and  it  was  early  suggested  that  plants  have  descended  from 
earlier  and  different  forms  through  modifications  of  structure. 
For  many  centuries  proofs  of  this  idea  accunuilated,  but  the 
whole  subject  did  not  receive  adequate  treatment  until  Charles 
Darwin  issued  his  "  Origin  of  Species  "  in  1859.  In  this  book 
was  gathered  a  great  mass  of  facts  in  support  of  the  conten- 
tion that  all  plants  and  animals  have  arisen  by  the  slow  proc- 
esses of  variation  and  natural  selection,  and  to  this  theory  of 
organic  descent  the  name  of  the  Danvinian  theory  has  come 
to  be  applied. 

Mutation  theory.  As  the  study  of  nature  has  progressed, 
many  instances  of  evolution  have  been  encountered  that  are 
difficult  to  reconcile  with  the  Darwmian  theory.  While  the 
mam  features  of  evolution  have  not  been  questioned,  there 
has  seemed  to  be  need  of  additional  explanations  to  account 
for  the  origin  of  certain  forms  which  it  is  difficult  to  imagine 
could  be  produced  by  gradual  changes.  These  are  supplied  by 
the  mutation  theory  of  Hugo  De  Vries.  This  new  theory  does 
not  take  the  place  of  the  Darwinian  theory  but  rather  sup- 
plements it.  The  new  theory  holds  that  new  species  do  not 
always  arise  from  old  ones  by  a  succession  of  slight  modifica- 
tions, but  that  they  may  spring  into  being  fully  developed, 
much  as  sports  and  bud  variations  appear  among  cultivated 
plants.  This  theory  is  capable  of  experimental  proof,  and  De 
Vries  has  produced  a  number  of  distinct  forms  from  a  single 


276  AGRONOMY 

sowing  of  seeds  of  certain  species.  Following  this,  it  has  been 
shown  that  many  of  what  the  botanist  calls  species  are  made 
up  of  numerous  simpler  forms  grouped  around  a  certam  type. 
These  forms  are  known  as  elementary  species  and  agree  pretty 
closely  with  what  the  gardener  calls  forms  or  varieties.  Ele- 
mentary species  may  be  separated  out  of  the  botanical  species 
by  breeding.  More  than  two  hundred  such  forms  have  been 
produced  in  Europe  from  the  species  called  Draha  vema.  It 
is  supposed  that  many  plants  are  constantly  throwing  off  such 
forms,  but  owing  to  the  crowd  of  plants  better  adapted  to 
the  locality,  these  seldom  have  a  chance  to  mature.  New 
forms  are  able  to  persist  only  when  they  are  better  adapted 
to  their  habitat  than  their  parents  are.  It  therefore  appears 
that  species  have  arisen  by  either  of  two  methods  —  by  slow 
modifications  or  by  sudden  sports,  or  mutations.  Having  arisen, 
however,  they  at  once  fall  under  the  influences  that  result  in 
further  change,  and  so  long  as  their  development  is  in  harmony 
with  their  position  in  life,  so  long  will  they  exist  to  carry  on 
the  family  line. 

PRACTICAL  EXERCISES 

1.  In  spring  visit  a  weed  patch,  a  neglected  garden,  or  other  waste 
ground,  and  note  the  number  of  seedlings  springing  up.  See  if  you  can 
discover  any  that  are  leading  in  the  race  for  light  and  air.  What  do 
you  think  gave  them  this  lead  ? 

2.  Measure  off  a  square  yard  on  the  lawn  or  in  a  pasture  and  count 
and  name  the  different  kinds  of  plants  found  growing  in  it. 

3.  Take  any  abundant  plant  and  count  the  seeds  produced  by  a 
single  specimen.  If  each  seed  produced  a  mature  plant  capable  of  ripen- 
ing a  similar  number  of  seeds,  how  many  years  would  it  take  to  produce 
one  plant  for  each  square  foot  of  soil  in  the  world  ?  Why  does  not  your 
particular  plant  become  as  abundant  as  this  ?    Give  two  reasons. 

References 

Darwin,  "The  Origin  of  Species." 
De  Vries,  "The  Mutation  Theory." 
Vernon,  "  Variation  in  Animals  and  Plants." 


CHAPTER  XX 

OUR  CULTIVATED  PLANTS 

Origin.  It  is  a  matter  of  common  knowledge  that  all  the 
plants  at  present  cultivated  in  the  world  have  been  derived 
from  wild  ancestors.  In  some  cases  the  very  species  from 
which  they  originated  are  still  in  existence,  but  more  fre- 
quently the  plants  have  been  so  long  in  cultivation,  or  have 
been  so  greatly  changed  by  this  process,  that  the  species  from 
which  they  have  been  derived  are  not  to  be  recognized,  and 
even  the  place  of  origin  of  some  is  unknown.  The  manner  in 
which  the  selection  of  these  plants  first  began  is  easily  imagined. 
Owing  to  the  tendency  of  plants  to  vary,  there  must  always 
have  appeared,  here  and  there  in  the  wild,  plants  that  bore 
superior  fruits  and  seeds.  These  even  the  wild  man  would 
prefer  and  in  time  would  come  to  protect  both  from  the 
encroachments  of  less  desirable  plants  and  from  other  wild 
men  who  might  wish  to  appropriate  them.  When  it  occurred 
to  some  genius  of  that  far-off  time  that  the  valued  plant  could 
be  better  protected  by  removing  it  to  the  vicinity  of  his  hut, 
agriculture  may  be  said  to  have  begun.  As  more  and  more 
plants  came  to  be  protected  in  this  way,  the  best  were  naturally 
selected,  and  so  through  hundreds  or  thousands  of  years  our 
grains  have  been  bred  from  wild  grasses,  our  potherbs  from 
thick-leaved  species  with  edible  qualities,  our  fruits  from  the 
smaller,  less  juicy,  and  poorly  flavored  forms  of  wood  and 
glen,  and  our  seed  crops  from  those  plants  which,  either  by 
reason  of  their  size,  abundance,  or  the  ease  with  which  they 
are  gathered,  offered  a  promising  field  for  the  grower.  The 
work  has  undoubtedly  been  helped  along  by  sports  that  have 

277 


278  AGRONOMY 

occurred  from  time  to  time,  both  in  cultivation  and  in  the 
wild,  and  which  have  brought  to  the  gardener  much  better 
varieties  than  he  could  produce  by  years  of  selection. 

Edible  parts  of  plants.  Instances  are  comparatively  few  in 
which  the  entire  plant  is  used  for  food.  Young  beets  and  tur- 
nips are  often  used  in  this  manner  £is  potherbs,  but  usually 
only  a  part  of  each  plant  is  considered  edible.  Ripe  fruits  are 
the  only  parts  that  seem  to  have  been  made  to  be  eaten.  The 
juicy  pulp  that  surrounds  the  seeds  of  some  species  is  sup- 
posed to  have  been  developed  for  the  purpose  of  attractmg 
animals  and  thus  securing  the  distribution  of  the  seeds ;  but 
when  we  eat  the  seeds  themselves,  as  in  the  case  of  peas  and 
beans,  or  the  roots,  stems,  and  leaves  of  other  species,  we  take 
what  the  plant  has  laid  by  for  itself.  There  is  scarcely  a  plant 
part,  however,  that  man  does  not  find  edible  in  some  species. 
In  practically  every  instance,  no  matter  what  part  is  used,  it 
will  be  found  to  be  that  in  which  the  plant  stores  its  reserve 
food.  In  the  carrot,  parsnip,  salsify,  and  radish  it  is  the  root 
that  is  eaten ;  indeed,  the  word  "  radish  "  is  derived  from  a 
Latin  word  meaning  ''root."  Stems  in  general  are  too  tough  to 
be  palatable,  but  we  must  not  overlook  in  this  connection  the 
young  stems  of  asparagus,  the  swollen  stems  of  kohl-rabi,  or 
the  underground  stems  of  the  potato  and  Jerusalem  artichoke. 
Lettuce,  endive,  chard,  spinach,  and  cabbage  are  good  examples 
of  plants  that  are  eaten  for  their  leaves,  while  several  others 
are  valued  for  their  leafstalks  or  petioles  alone,  among  which 
may  be  mentioned  rhubarb,  celery,  and  sea  kale.  The  young 
flower  buds  form  the  edible  parts  of  the  cauliflower  and  globe 
artichoke.  Peas  and  beans  are  true  seeds,  but  the  grain  of 
corn  is  a  fruit,  and  so  are  melons,  tomatoes,  and  peppers.  The 
greengrocer  usually  divides  his  wares  into  the  two  groups, 
fruits  and  vegetables,  and  while  there  can  be  no  question  about 
the  vegetables,  since  even  the  fruits  are  vegetable  in  origin, 
many  of  the  things  he  calls  vegetables  are  certainly  fruits  also. 


OUR  CULTIVATED  PLANTS  279 

Root  crops.  Most  of  our  plants  with  edible  roots  are  little 
changed  from  the  originals.  This  is  quite  natural,  since  the 
only  improvement  desired  has  been  the  increased  size  of  the 
roots  and  a  greater  storage  of  food.  The  heet  is  a  native  of 
the  Mediterranean  region  and  still  grows  wild  there  and  as 
far  east  as  Persia.  The  carrot,  turnip,  parsnip,  and  radish  are 
found  in  southern  and  central  Europe,  and,  all  but  the  turnip, 
having  escaped  from  cultivation  in  this  country,  have  shown 
themselves  able  to  maintain  an  existence  in  the  wild  state. 
Salsify,  or  vegetable  oyster,  like  the  beet,  still  grows  wild  in  the 
Mediterranean  region.  From  the  garden  beet  \\\e  field  ov  sugar 
heet  has  arisen,  and  from  the  turnip  comes  the  rutabaga.  The 
potato,  though  in  no  sense  a  root,  is  usually  classed  with  the 
root  crops.  It  is  a  native  of  western  South  America,  where 
its  relatives  still  abound.  It  was  cultivated  by  the  natives  of 
the  region  before  the  discovery  of  America,  but  does  not  seem 
to  have  been  known  to  the  North  American  Indians.  The  sweet 
potato  is  a  true  root,  the  product  of  a  plant  belonging  to  the 
mornmg-glory  family.  It  is  regarded  as  a  native  of  South 
America,  but  has  long  been  in  cultivation  in  China  and  is 
thought  by  some  to  have  had  a  separate  origin  in  each  country. 
The  Jerusalem  artichoke  is  a  species  of  sunflower,  which  grows 
wild  in  the  Northern  states  and  Canada,  and  was  occasionally 
cultivated  by  the  Indians  before  the  advent  of  the  whites. 

Leaf  crops.  Chief  of  the  plants  grown  for  their  leaves  is  the 
cabbage,  which  is  still  found  in  the  wild  state  in  the  south  of 
England,  the  Channel  Islands,  and  on  the  shores  of  the  North 
Sea.  The  wild  plant  has  thickish  leaves,  but  it  is  quite  unlike 
the  hard-headed  specimens  of  our  gardens.  From  this  same 
plant  has  come  a  long  list  of  varieties  that  are  valued  in  cul- 
tivation, such  as  kale,  cauliflower,  Brussels  sprouts,  kohl-rabi, 
and  the  like.  Lettuce  came  originally  from  the  jNIediterranean 
region,  but  is  now  widely  distributed  in  both  the  Old  World 
and  the  New  as  a  pernicious  weed.    It  is  not  easy  to  realize 


280  AGRONOMY 

that  the  weedy,  prickly  lettuce  of  waste  places  and  neglected 
gardens  is  the  same  species  as  the  tender,  smooth-leaved,  solid- 
headed  plant  so  highly  valued  in  cultivation.  The  lettuce 
was  once  grown  for  its  loose  leaves,  which  were  little  changed 
from  the  original,  but  nowadays  it  has  been  bred  to  make  solid 
heads  like  a  cabbage.  The  spinach,  which  much  resembles  the 
lettuce  in  form,  has  been  known  since  earliest  times.  It  is  a 
native  of  Persia.  The  onion  is  another  species  valued  for  its 
edible  leaves,  though  many  think  the  bulbous  part  is  a  root. 
It  is,  however,  a  true  bulb  made  up  of  the  thickened  bases  of 
the  leaves.  The  cultivated  onion  is  a  native  of  western  Asia 
and  has  been  known  for  centuries.  IVIany  other  species  grow 
wild  in  both  Europe  and  America.  The  leek  is  a  species  of 
onion  and  grows  wild  on  both  sides  of  the  Atlantic.  Celery 
has  long  been  m  cultivation,  but  may  still  be  found  wild  in 
parts  of  Europe  and  western  Asia.  It  belongs  to  the  same 
plant  family  as  the  parsley,  parsnip,  carrot,  fennel,  dill,  corian- 
der, and  other  species  valued  for  their  aromatic  seeds.  Aspara- 
gus, though  not  a  leaf  crop,  may  be  mentioned  in  this  connec- 
tion. It  has  been  cultivated  for  many  centuries,  and  is,  of 
course,  a  native  of  the  Old  World.  In  the  wild  state  the 
stems  of  asparagus  are  rather  slender,  but  under  proper  cul- 
tivation they  reach  a  diameter  of  more  than  an  inch. 

The  legumes.  Some  species  of  legumes  seem  to  have  been 
among  the  first  plants  cultivated  by  man.  The  seeds  of  peas 
and  lentils  have  been  found  among  materials  referred  to  the 
Bronze  Age  of  Europe.  The  word  "  legume  "  comes  from  the 
Latin  legere,  meaning  "  to  gather,"  and  seems  originally  to 
have  been  applied  to  any  species  of  plant  gathered  by  hand. 
The  seeds  of  the  plants  now  called  legumes  were  usually  prom- 
inent in  such  gathered  crops,  and  the  name  has  since  come  to 
be  restricted  to  them.  The  lentil,  little  grown  in  America,  has 
long  been  cultivated  in  the  warmer  parts  of  the  Old  World, 
especially   in   the   Mediterranean   region,    and   the  pea  has 


OUR  CULTIVATED  PLANTS  281 

probably  been  derived  from  a  wild  species  growing  in  the 
same  region.  Beans,  at  least  the  common  varieties,  have  come 
from  South  America.  The  soy  bean  and  cowpea  are  natives 
of  China. 

Solanaceous  fruits.  Several  edible  fruits  are  produced  by 
the  nightshade  family  (Solanaceae).  This  family  contains 
many  poisonous  species,  though  the  fruits  are  usually  edible. 
In  addition  to  the  food  plants,  the  family  contains  the  tobacco 
plant  and  the  petunia.  Of  the  species  grown  for  their  fruits 
the  tomato  takes  first  place,  although  the  latest  of  the  group 
to  be  used  as  food.  Less  than  a  hundred  years  ago  it  was  re- 
garded as  poisonous  and  was  grown  only  for  ornament  under 
the  name  of  love  apple.  The  tomato  is  still  found  wild  in  its 
native  land,  Peru,  but  is  now  grown  almost  the  world  over. 
The  fruit  has  been  greatly  increased  in  size  by  cultivation. 
The  red  pepper,  husk  tomato,  and  eggplant  are  relatives  of  the 
tomato.  The  first  two  are  of  American  origin ;  the  last  is  said 
to  be  a  native  of  southwestern  Asia.  The  ivonderherry,  or 
garden  huckleberry,  is  a  species  of  nightshade  developed  from 
a  common  weed  in  the  central  and  western  states.  It  may  be 
mentioned  in  this  connection  that  the  potato  is  the  enlarged 
underground  stem  of  another  species  of  nightshade. 

Gourd  fruits.  Some  species  of  the  gourd  family  are  poison- 
ous or  unfit  for  food,  but  the  group  also  contains  a  large  num- 
ber of  edible  species.  They  all  have  long  and  weak  stems  that 
spread  out  over  the  ground  or  climb  on  other  plants,  trellises, 
and  the  like.  The  encumber  is  one  of  the  oldest  of  this  group 
in  cultivation,  having  been  known  in  China  for  quite  three 
thousand  years.  The  melons  are  natives  of  Africa.  The  water- 
melon still  grows  wild  in  central  Africa,  and  the  muskmelon 
extends  eastward  and  northward  to  western  Asia.  The  pump- 
kin is  a  native  of  America,  and  was  cultivated  by  the  Indian 
in  his  cornfields  at  the  time  of  the  discovery  of  the  continent, 
just  as  it  is  still  cultivated. 


282  AGRONOMY 

The  grasses.  With  the  exception  of  maize,  or  Indian  com^ 
all  the  grasses  cultivated  for  food  are  natives  of  the  Old 
World.  The  list  includes  wheat,  oats,  harley,  rye,  millet,  sugar 
cane,  sorghum,  and  rice.  The  grains  have  been  cultivated  so 
long  that  the  origin  of  most  of  them  is  lost  in  antiquity. 
Wheat  has  been  cultivated  at  least  five  thousand  years.  Rice, 
though  cultivated  in  ancient  times,  still  exists  in  the  wild 
state,  but  it  is  a  question  whether  wild  wheat  can  now  be 
found.  Indian  corn  is  a  product  of  the  warmer  parts  of  the 
New  World  and  was  cultivated  by  the  Indians  long  before  the 
time  of  Columbus.  It  is  not  native  to  the  Old  World.  Eng- 
lishmen use  the  word  "  corn  "  for  several  kinds  of  grain,  and 
when  references  to  corn  are  encountered  in  early  English  liter- 
ature and  in  the  Bible,  it  should  be  understood  that  the  grain 
we  call  corn  is  not  the  one  meant. 

Bush  fruits.  All  the  common  bush  fruits,  raspberries,  black- 
berries, currants,  gooseberries,  and  the  like,  grow  wild  in  both 
Europe  and  America.  Some  of  the  species  in  cultivation  are 
of  Old  World  origin,  others  have  originated  on  this  side  of 
the  world,  and  some  are  hybrids  between  them.  They  are 
usually  but  little  changed  from  their  wild  relatives,  the  most 
noticeable  difference  being  found,  as  would  be  expected,  in 
the  larger  fruits. 

Tree  fruits.  Our  tree  fruits  are  all  closely  related  and  be- 
long to  groups  allied  to  the  rose  family.  They  have  been 
cultivated  from  the  earliest  times  and  are  much  modified  in 
consequence.  The  apple,  cherry,  and  peach  are  natives  of 
western  or  southern  Asia,  the  pear  comes  from  Europe,  and 
the  different  species  of  plums  are  found  both  in  Europe  and 
America.  The  grape,  while  not  a  tree  fruit,  may  be  mentioned 
here.  Nearly  all  the  common  varieties  cultivated  in  eastern 
and  southern  North  America  have  originated  from  native 
species.  The  European  grapes  do  not  thrive  in  the  eastern 
states,  but  are  extensively  grown  on  the  Pacific  coast. 


OUR  CULTIVATED  PLANTS  283 

New  fruits.  That  there  are  many  other  plants  in  the  wild 
which  might  be  made  to  take  the  place  of  plants  now  culti- 
vated is  beyond  question.  Those  that  have  been  developed 
are  without  doubt  those  that  first  came  to  hand  in  a  promis- 
ing form,  but  many  still  remain  that,  with  the  same  amount 
of  care  in  developing,  would  yield  equally  valuable  results. 
We  neglect  the  common  elderberry,  the  wild  crab,  the  many 
species  of  hawthorn,  the  papaw,  the  persimmon,  wild  rice,  and 
many  others  simply  because  we  have  other  species  as  good. 
The  huckleberries  and  blueberries  are  just  bemg  brought  under 
cultivation,  and  the  cranberry  is  essentially  wild,  though  cared 
for  and  even  planted  in  bogs  suited  to  its  requirements. 
Even  in  the  wild  state  these  are  very  desirable  plants.  Call- 
ing to  mind,  however,  the  advances  made  by  other  fruits  when 
carefully  cultivated  and  selected,  it  seems  likely  that  these 
and  many  others  may  yet  be  made  to  yield  much  finer  fruits 
than  they  now  produce. 

PRACTICAL  EXERCISES 

1.  Make  a  list  of  the  wild  fruits,  seeds,  roots,  and  leaves  that  you 
know  are  edible. 

2.  Make  a  list  of  the  wild  plants  with  which  you  are  familiar  that 
are  related  to  cultivated  crops. 

3.  Make  a  list  of  wild  species  that  you  think  would  be  valuable  for 
domestication. 

4.  What  do  you  conclude  to  be  the  greatest  obstacle  to  introducing 
them  into  cultivation  ? 

References 

Bailey,  "  Evolution  of  our  Native  Fruits." 

Bailey,  "  Survival  of  the  Unlike." 

Davenport,  "  Domesticated  Animals  and  Plants." 

De  Candolle,  "Origin  of  Cultivated  Plants." 

De  Vries,  "  Species  and  Varieties  ;  their  Origin  by  Mutation." 

Sargent,  "Corn  Plants." 

"Willis,  "A  Practical  Flora." 


APPENDIX 

SEVENTY-FIVE  SHRUBS  USEFUL  FOR  PLANTING 

[With  notes  on  their  height,  color,  time  of  hlooming,  etc.] 

Alder,  white  {Clethra  alnifolia)  :  4-10  feet ;  white  ;  summer ;  flowers  very 
fragrant. 

Almond,  flowering  (Prunus  Japonica) :  3-5  feet ;  pinkish  ;  spring. 

Ash,  prickly  {Zanthoxylum  Americanum) :  6-8  feet ;  yellowish  ;  spring. 

Azalea  {Azalea  nudiflora)  :  6-15  feet ;  pink  ;  spring. 

Barberry  {Berberis  vulgaris)  :  4-7  feet ;  yellow  ;  spring ;  stems  thorny  ; 
fruit  scarlet,  persisting  into  the  winter  ;  used  for  jelly. 

Barberry,  Japanese  {Berberis  Thunbergii)  :  2-4  feet ;  yellowish ;  spring ; 
thorny  stems;  fruit  scarlet,  in  small  clusters,  persistent;  much  used  for 
low  hedges. 

Barberry,  purple  {Berberis  vulgaris  var.  purpurea) :  4-6  feet ;  yellowish ; 
spring  ;  leaves  purple-tinged  ;  used  for  hedges. 

Bladder  nut  {Staphylea  trifolia)  :  6-12  feet ;  white  ;  spring ;  pods  large, 
three-angled,  inflated  ;  flowers  in  racemes. 

Box  {Buxus  sempervirens)  :  4-6  feet ;  greenish  ;  spring  ;  leaves  small,  ever- 
green ;  much  used  for  hedges. 

Buckthorn  (Rhamnus  cathartica)  :  8-12  feet ;  whitish  ;  spring  ;  thorny  and 
much  used  for  hedges  ;  fruit  black. 

Buffalo  berry  {Shepherdia  argentea)  :  6-8  feet ;  yellowish  ;  late  spring  ;  fruit 
red,  edible  ;  leaves  silvery-scaly  beneath. 

Burning  bush  {Euonymus  atropurpureus)  :  8-12  feet ;  purplish- red  ;  early 
summer ;  fruit  pale  pink,  at  length  splitting  and  showing  the  scarlet  aril 
which  surrounds  the  seed. 

Button  bush  {Cephalanthus  occidentalis)  :  4-10  feet ;  white  ;  summer  ;  flow- 
ers in  globular  heads,  fragrant ;  good  for  planting  in  wet  places. 

Chokeberry  {Pyrus  arbuiifolia)  :  3-8  feet ;  pinkish  ;  early  summer. 

Cinquefoil,  shrubby  {Potentilla  fruticosa)  :  1-3  feet ;  yellow  ;  early  summer; 
foliage  grayish  ;  does  well  in  dry  situations. 

Coralberry  {Symphoricarpos  vulgaris)  :  2-4  feet ;  pink  ;  summer  ;  fruit  coral 
red  ;  plant  desirable  for  dry  banks  ;  spreads  by  stolons. 

Crab,  wild  {Pyrus  coronaria) :  8-15  feet;  pink;  early  summer;  fruit  fra- 
grant, hard,  and  sour  ;  used  for  preserves. 

Cranberry,  high-bush  {Viburnum  opulus)  :  6-12  feet;  white;  late  spring; 
fruit  red,  persistent ;  regarded  as  the  parent  of  the  snowball  tree. 

285 


286  AGRONOMY 

Currant,  flowering  {Ribes  aureum) :  4-8  feet ;  yellow  ;  early  spring  ;  flower 
very  strongly  spicy-scented  ;  fruit  black. 

Currant,  wild  {liibes floridum)  :  3-7  feet ;  greenish  ;  early  spring. 

Daphne  (Daphne  mezereum) :  1-4  feet ;  rose-purple  or  white  ;  early  spring ; 
flowers  appear  before  the  leaves. 

Deutzia  (Deutzia  scabra) :  4-6  feet ;  white  ;  late  spring  ;  leaves  sprinkled 
with  stellate  hairs. 

Deutzia,  small  (Deutzia  gracilis)  :  2-3  feet ;  white  ;  spring  ;  much  used  for 
low  borders. 

Dogwood,  or  red  osier  (Comus  stolonifera) :  4-8  feet ;  white  ;  early  summer ; 
stems  dark  red,  very  showy  in  winter  ;  spreads  by  stolons. 

Eldei, common  (Sambucus Canadensis):  6-12 feet;  creamy  white;  early  sum- 
mer ;  valued  alike  for  its  large  panicles  of  flowers  and  for  its  purplish-black 
fruit ;  medicinal ;  several  variegated  and  cut-leaved  forms  are  known. 

Elder,  red-berried  (Sambucus  pubens)  :  6-10  feet ;  greenish  ;  spring  ;  berries 
bright  red,  ripening  in  early  summer  at  the  time  the  preceding  species  is 
blooming  ;  several  cut-leaved  forms  ai-e  cultivated. 

Fringe  tree  (Chionanthus  Virginica)  :  7-10  feet ;  white  ;  spring. 

Golden  bell  (Forsythia  suspensa)  :  6-8  feet ;  bright  yellow  ;  early  spring ; 
flowers  appear  before  the  leaves  and  cluster  thickly  along  the  branches ; 
one  of  our  most  decorative  species  ;  branches  drooping. 

Goldenhell  (Forsythia  viridissima)  :  6-12  feet ;  yellow;  early  spring  ;  more 
erect  than  the  preceding. 

Gooseberry,  early  (Ribes  gracilis)  :  3-6  feet ;  pale  yellow  ;  early  spring  ;  the 
first  shrub  to  put  forth  leaves  in  spring  ;  thorny  ;  much  used  for  hedges. 

Hardback  (Spiraea  tomentosa)  :  1-3  feet ;  pink  ;  summer. 

Hawthorn  (Crataegus  sp.)  :  10-15  feet ;  white  ;  spring. 

Hazel  (Corylus  sp.)  :  6-12  feet ;  yellow  and  red  ;  early  spring  ;  the  flowers 
are  borne  in  catkins  and  are  among  the  first  to  appear  in  spring ;  the  fruit 
is  the  well-known  filbert. 

Honeysuckle,  Tartarian  (Lonicera  Tatarica) :  6-10  feet ;  pink  ;  late  spring ; 
red  berries. 

Hop  tree  (Ptelia  trifolia)  :  6-12  feet ;  greenish ;  early  summer ;  flowers 
sweet  scented  ;  fruits  round,  broad-winged. 

Hydrangea  (Hydrangea  paniculata)  :  4-8  feet ;  white  ;  summer. 

Jersey  tea  (Ceanothus  Americanus)  :  1-3  feet ;  pale  cream  ;  early  summer  ; 
excellent  for  dry  places  ;  the  feathery  flower  clusters  are  borne  in  profusion  ; 
seeds  are  thrown  long  distances  by  the  splitting  of  the  pod ;  the  young 
seed  pods  contain  much  vegetable  soap. 

June  berry  (Amelanchier  sp.)  :  6-20  feet ;  white  ;  early  spring  ;  fruit  red 
or  blackish,  sweet,  and  edible. 

Kerria  (Kerria  Japonica)  :  3-5  feet ;  orange-yellow  ;  early  summer  ;  twigs 
bright  green  in  winter. 

Kerria,  white  (Rhodotypus  kerrioides)  :  3-6  feet ;  white  ;  early  summer. 

Laurel,  mountain  (Kalmia  latifolia)  :  2-8  feet ;  pinkish  ;  early  siunmer. 

Leadwort  (Amorpha  fruticosa) :  4-6  feet ;  pui-plish  ;  summer. 


APPENDIX  287 

Leatherwood  {Dirca  palustris)  :  3-6  feet ;  yellow  ;  early  spring ;  excel- 
lent for  wet  places ;  flowers  appearing  with  the  leaves  ;  bark  exceedingly 
tough. 

Lilac,  common  (Syringa  vulgaris)  :  8-15  feet ;  purple  or  white  ;  early  spring. 

Lilac,  Persian  {Syringa  Persica)  :  8-15  feet ;  purple  ;  spring  ;  more  spread- 
ing than  the  preceding  species. 

Ninebark  (Physocarpus  ■  opulifolius)  :  6-12  feet  ;  white  ;  early  summer  ; 
flowers  like  those  of  the  spirteas ;  bark  shed  in  long  strings ;  medicinal. 

Olive,  Russian  {Elceagnus  angustifolius)  :  8-15  feet;  cream  color;  early 
summer ;  leaves  silvery  white  from  the  numerous  scales ;  fruit  silvery. 

Osier,  European  {Cornus  sanguinea)  :  4-8  feet ;  white  ;  early  summer ; 
stems  deep  red  ;  a  form  with  white-edged  leaves  is  common. 

Pea  bush  {Desmodium  penduUflonim)  :  4-5  feet ;  rose-purple  ;  autumn. 

Pea  tree,  Siberian  (Caragana  arborescens)  :  10-15  feet ;  yellow  ;  spring. 

Pearl  bush  {Exochorda  grandifiora)  :  6-12  feet ;  white  ;  spring. 

Privet  {Ligustrum  sp.)  :  4-12  feet ;  white  ;  summer ;  nearly  evergreen  ; 
the  various  species  are  much  used  for  hedges. 

Quince,  Japanese  {Cydonia  Japonica)  :  6-10  feet ;  bright  red  ;  early  spring  ; 
flowers  appearing  with  the  leaves  ;  shrub  thorny. 

Raspberry,  flowering  {Rubus  odoratus)  :  2-5  feet ;  purple  ;  summer  ;  thorn- 
less  ;  leaves  large,  lobed  ;  fruit  insipid. 

Rhododendron  {Rhododendron  sp.)  :  6-12  feet ;  white  to  pink  ;  summer. 

Rose  of  Sharon  {Hibiscus  Syriacus)  :  8-12  feet ;  white  to  red  ;  late  summer  ; 
very  attractive,  the  flowers  like  hollyhocks. 

Senna,  bladder  {Colutea  arborescens)  :  8-10  feet ;  yellow ;  early  summer ; 
pods  inflated. 

Sheepberry  {Viburnum  leniago)  :  6-12  feet ;  white;  summer;  fruit  black, 
edible. 

Silver  bell  {Halesia  tetraphylla)  :  8-15  feet ;  white  ;  spring  ;  the  bell-shaped 
flowers  are  succeeded  by  curious  four-angled  and  winged  fruits. 

Smoke  tree  {Rhus  cotinus)  :  8-15  feet ;  greenish  ;  spring  ;  the  smoke-like 
masses  regarded  by  many  as  flowers  are  really  flower  stalks. 

Snowball,  Japanese  ( Viburnum  plicatum) :  6-10  feet ;  white  ;  early  summer  ; 
the  flower  clusters  consist  of  sterile  flowers,  and  the  whole  plant  resembles 
the  common  snowball,  or  guelder-rose. 

Snowberry  {Symphoricarpos  racemosus)  :  2-5  feet ;  pink  ;  summer  ;  fruit 
white,  persisting  into  the  winter. 

Spicebush  {Benzoin  odoriferum) :  6-10  feet;  yellow  ;  early  spring;  flowers 
appear  with  the  leaves  ;  bark  spicy. 

Spiraea  {Spiraea  sp.)  :  6-8  feet ;  white  ;  early  summer  ;  the  various  species 
of  spiraea  are  among  our  most  decorative  plants. 

Spiraea,  blue  {Caryopteris  maslacanlhus) :  2-4  feet ;  bright  blue  ;  late  sum- 
mer ;  has  the  appearance  of  a  spii'sea,  whence  the  common  name. 

Sumac,  common  {Rhus  glabra  and  R.  typhinia)  :  5-15  feet ;  greenish ; 
early  summer ;  foliage  turns  brilliant  crimson  in  autumn  ;  fruits  acid, 
edible ;  sevei'al  cut-leaved  varieties  occur. 


288  AGRONOMY 

Sumac,  fragrant  {Rhus  aromatica) :  3-6  feet ;  yellow  ;  spring ;  flowers  in 
catkins  appearing  before  tlie  leaves ;  f rnits  red,  edible. 

Sumac,  varnish  {Rhus  copalUna)  :  3-6  feet ;  greenish  ;  summer ;  leaves 
brilliant  red  in  autumn ;  good  slii-ub  for  dry  places. 

Sweet  shrub  {Calycanthus  floridus) :  3-8  feet ;  brownish-purple ;  late 
spring ;  flowers  very  fragrant  when  wilted,  and  of  an  unusual  color. 

Syringa,  mock  orange  {Philadelphus  coronarius)  :  6-10  feet ;  cream  color ; 
late  spring ;  flowei-s  very  fragrant ;  several  other  species  are  cultivated. 

Tamarisk  {Tamarix  sp.)  :  10-15  feet;  pinkish;  summer;  flowers  and 
leaves  small ;  branches  wandlike. 

Weigela  { Weigela  rosea)  :  4-6  feet ;  rose  color  ;  summer. 

Willow,  goat  {Salix  caprea) :  6-10  feet ;  yellowish ;  spring ;  has  immense 
catkins  of  flowers  that  appear  in  earliest  spring. 

Winterberry  {Ilex  verticillata)  :  3-8  feet ;  white ;  summer ;  a  hardy  decid- 
uous holly  with  red  berries  that  last  through  the  winter ;  excellent  for  wet 
places. 

Witch  hazel  {Hamamelis  Virginiana) :  6-12  feet ;  yellow  ;  late  autumn  ; 
blooms  as  tlie  leaves  are  falling ;  seeds  propelled  for  long  distances ;  plant 
much  used  in  medicine. 


fiftep:n  woody  vines  desirable  for  arbors  and 

PORCHES 

Bittersweet  {Celastrus  scandens) :  twiner ;  capsules  orange-yellow,  split- 
ting at  maturity  and  showing  the  scarlet  arils. 

Clematis,  panicled  {Clematis  paniculata)  :  climbs  by  twining  leafstalks ; 
flowers  white,  borne  in  great  profusion. 

Clematis,  purple  {Clematis  lanuginosa)  :  climbs  like  the  preceding ;  flowers 
large,  purple,  very  showy. 

Creeper,  trumpet  {Tecoma  radicans) :  half  twiner;  flowei*s  large,  tubular, 
dull  orange-red  ;  seeds  winged. 

Dutchman's  pipe  {Aristolochia  macrophylla) :  twiner ;  flowers  shaped  like 
a  pipe  ;  leaves  large,  making  a  dense  shade. 

Grape,  wild  {Vitis  sp.)  :  tendril  climbers  ;  any  of  the  wild  grapes  are  desir- 
able for  covering  arbors  and  trellises  ;  fruit  makes  excellent  jelly  and  wine. 

Honeysuckle,  Hall's  {Lonicera  Halliana)  :  twiner ;  flowei-s  white  turning 
yellow,  very  fragrant. 

Honeysuckle,  trumpet  {Lonicera  sempervirens) :  twiner ;  flowers  long, 
slender,  trumpet  shaped,  scarlet. 

Ivy,  Boston  {Ampelopsis  tricuspidata)  :  tendril  climber,  holding  fast  by 
small  disks  at  the  tips  of  the  tendrils  ;  will  cling  to  walls  of  any  kind. 

Matrimony  vine  {Lycium  vulgare)  :  half  twiner ;  stem  thorny ;  flowers 
purplish  ;  fruit  red,  inedible. 

Rose,  climbing  {Rosa  sp.) :  climbing  by  means  of  recurved  prickles ;  several 
species  are  useful  for  covering  arbors,  pillars,  and  porches. 


APPENDIX  289 

Virgin's-bower  {Clematis  Virginiana)  :  climbing  by  twining  leafstalks ; 
flowers  numerous,  white  ;  fruit  with  downy  appendages. 

Wistaria  ( Wistaria  Sinensis)  :  twiner ;  flowers  blue  or  white  in  large 
clusters,  very  showy. 

Woodbine,  common  {Ampelopsis  quinquefolia)  :  tendril  climber  ;  fruit  bluish- 
black,  inedible. 

Woodbine,  Western  {Ampelopsis  Engelmanni)  :  like  the  common  woodbine, 
but  tendrils  tipped  with  disks  that  cling  closely  to  supports  of  all  kinds. 


FIFTY  DESIRABLE  HERBACEOUS  PERENNIALS 

Aconite  {Aconitum  napellus)  :  3-4  feet ;  deep  blue  ;  summer. 

Amsonia  {Amsonia  labernamoniana)  :  2-3  feet ;  blue  ;  early  summer. 

Aster,  New  England  {Aster  Novan-Angliai) :  3-6  feet ;  purple  or  pink ; 
autumn. 

Baby's  breath  {Gypsophila  paniculata)  :  2-3  feet ;  white;  spring. 

Baptisia  {Bapiisla  australis)  :  2-3  feet ;  blue  ;  early  summer. 

Beardtongue  {Pentstemon  sp.)  :  2-3  feet ;  wliite  to  red  ;  summer. 

Bellflower,  Chinese  {Platycodon  grandifioi-um)  :  2-3  feet ;  blue  ©r  white  ; 
sunnner. 

Black-eyed  Susan  {Rudbeckia  triloba,  E.  hirta,  and  R.  speciosa)  :  1-3  feet ; 
yellow  and  black  ;  summer  and  autunni. 

Blanket  flower  {Gaillardia  aristata)  :  1-2  feet ;  red  and  yellow  ;  summer 
and  autunm. 

Bleeding  heart  {Dicentra  spectabilis)  :  2-3  feet ;  pink  ;  early  spring. 

Bluebells  {Meriensia  Virginica)  :  2-3  feet ;  sky  blue  ;  spring. 

Boltonia  {Boltonia  asteroides)  :  4-5  feet ;  white  ;  early  autumn. 

Butterfly  weed  {Asclepias  tuberosa)  :  1-2  feet ;  orange-yellow  ;  summer. 

Columbine  {Aquilegia  sp.)  :  2-3  feet ;  white  to  yellow  and  blue  ;  spring. 

Coneflower,  purple  {£"cAmacea  purpurea)  :  2-3  feet ;  purplish-red;  summer. 

Coreopsis  {Coreopsis  sp.)  :  2-3  feet ;  yellow  ;  summer. 

Dame's  violet  {Hesperis  matronalis)  :  1-2  feet ;  white  to  pink  ;  .spring. 

Golden  glow  {Rudbeckia  laciniata)  :  0-7  feet ;  yellow  ;  late  summer. 

Goldenrod  {Solidago  rigida  and  others)  :  3  feet ;  yellow  ;  late  sunnner. 

Harebell  {Campanula  Carpathica)  :  6-9  inches  ;  deep  blue  ;  summer. 

Hollyhock  {AlUma  rosea)  :  3-8  feet ;  white  to  red  and  yellow  ;  summer. 

Iris  {Iris  sp.)  :  1-3  feet ;  white  to  yellow  and  purple  ;  spring. 

Jacob's  ladder  {Polemonium  sp.)  :  1-2  feet ;  blue  ;  spring. 

Larkspur  {Delphinium  fonnosum) :  1-3  feet ;  deep  blue  ;  summer. 

Lilies  {Lilium  sp.)  :  2-4  feet ;  white  to  yellow  and  red  ;  sunnner. 

Lilies,  day  {Ileinerocallis  sp.) :  2-4  feet ;  orange,  golden  yellow,  and  dull 
red  ;  late  spring  and  summer. 

Lily  of  the  valley  {Convallaria  majalis)  :  6-9  inches  ;  white  ;  early  spring. 

Lily,  plantain  {Funkia  sp.)  :  1-1 J  feet ;  white  or  blue  ;  summer. 

Marsh  mallow  {Hibiscus  moscheutos) :  4-6  feet ;  white  and  pink ;  late  summer. 


290  AGRONOMY 

Mullein  {Verbascum  pannosum  and  V.  nigruin):  3-6  feet;  yellow;  early 
suniiiier. 

Obedient  plant  {Physostegia  Virginica) :  2-3  feet ;  pinkish  ;  summer. 

Oxeye  {lleliopsis  Icevis)  :  2-3  feet ;  copper-yellow  ;  summer. 

Pea,  perennial  {Lalhyrus  latifoliuH)  :  3-0  feet ;  pink  or  white ;  summer. 

Peony  (Pteonia  officinalis)  :  2-4  feet ;  white  to  red  ;  late  spring. 

Pheasant's  eye  {Adonis  vemalis)  :  6-9  inches ;  yellow  ;  early  spring. 

Phlox,  perennial  {Phlox  sp.) :  2-3  feet ;  white  to  red  and  purple  ;  summer 
and  autunin. 

Pink  moss  {Phlox  subulata) :  6  inches  ;  pink  ;  spring. 

Poppy,  mallow  {Callirhoe  involucrata)  :  6-9  inches  ;  rose-pink  ;  summer. 

Poppy,  perennial  {Papaver  orientale)  :  2-3  feet ;  red  ;  early  summer. 

Primrose,  evening  {Oenothera  sp.)  :  1-3  feet;  yellow  or  white  ;  summer. 

Pyrethrum  {Pyrethrum  hybridum)  :  1-3  feet ;  white  to  pink  ;  spring. 

5t.-John's-wort  {Hypericum  ascyron)  :  2-3  feet ;  yellow  ;  early  summer. 

Senna,  wild  {Cassia  Marylandica)  :  3-0  feet ;  yellow  ;  summer. 

Sneezeweed  {Helenium  autumnale)  :  3-0  feet ;  yellow  ;  summer. 

Sunflower  {Helianthus  sp.) :  0-10  feet ;  yellow  ;  late  summer  and  autumn. 

Sweet  flag  {Acorus  calamus)  :  2-3  feet ;  green  ;  summer. 

Sweet  William  {Dianthus  barbatus)  :  1-2  feet ;  white  to  pink  ;  sunnner. 

Sweet  William,  wild  {Phlox  divaricata)  :  1-2  feet ;  blue  ;  late  spring. 

Yarrow  {Achillea  pLarmica)  :  1-2  feet ;  wiiite  ;  early  summer. 

Yucca  {Yucca Jilamentosa) :  3-6  feet ;  cream  color  ;  summer. 


INDEX 


Absorption,  selective,  95 

Acclimatization,  115 

Acid  soils,  35  ;  effect  of  lime  on,  36  ; 

plants  of,  35  ;  test  for,  35 
Air,  40  ;  as  a  weathering  agent,  13  ; 

composition   of,   40 ;    in  soil,  41  ; 

moisture  in,  116  ;  value  of,  in  soil, 

41 ;    variations   in    pressure,    40 ; 

weight  of,  40 
Albumen,  86 
Alkali  soils,  34 
Aluminum,  characteristics  of,  7 ;  in 

plants,  100 
Ammonification,  107 
Amyloplasts,  77 
Annuals,  87  ;  value  of,  205 
Anthers,  79 
Arid  regions,  11 
Artificial  soils,  36 
Atoin,  definition  of,  2  ;  size  of,  2 

Bacteria,  and  nitrification,  107 ;  de- 
nitrifying, 110  ;  in  symbiosis,  108  ; 
need  of  lime,  109  ;  requirements 
for  growth,  107 

Bed  rock,  12 ;  modifications  of,  20 ; 
outcrops  of,  12 

Biennials,  87 

Blanching,  effects  of,  123 

"  Bleeding  "  of  plants,  97 

Borders,  arrangement  of  plants  in, 
202 ;  character  of,  201 

Bowlders,  31 

Bridge  grafting,  193 

Bud  scales,  69  ;  use  of,  69 

Bud  variations,  260 

Budding,  methods  of,  190  ;  uses  of, 
189 

Buds,  accessory,  67, 69  ;  adventitious, 
69;  dormant,  70;  flower,  70;  lat- 
eral, 67 ;  leaf,  70 ;  mixed,  70 ; 
naked,  69  ;  protection  of,  69  ;  ter- 
minal, 67 

Bulbs,  value  of,  207 


Bundles,  flbrovascular,  65 ;  arrange- 
ment in  dicotyledons,  66  ;  arrange- 
ment in  monocotyledons,  66 

Bushes,  89 

Calcium,  characteristics  of,  6;  test 
for,  in  soils,  105  ;  use  of,  by  plants, 
98 

Calcium  carbide,  4 

Calyx,  79 

Cambium,  in  roots,  61 ;  in  stems,  66, 67 

Carbohydrates,  98 

Carbon,  characteristics  of,  9 ;  occur- 
rence of,  97 

Carbon  dioxide,  amount  in  air,  97 ; 
formation  of,  4 

Carbon  disulphide,  4 

Carpels,  79 

Carpet  bedding,  208 

Caruncle,  86 

Cavities  in  trees,  228 

Cell,  57 

Cell  sap,  57 

Cell  wall,  57 

Centigrade  scale,  43 ;  rule  for  chang- 
ing, to  Fahrenheit,  43 

Chemical  compounds,  1,  4 

Chemical  elements,  change  of  state 
in,  2  ;  distribution  of,  5, 101 ;  found 
in  plants,  5 ;  in  plant  food,  75 ;  lack- 
ing in  soils,  104 ;  most  abundant,  5 ; 
native,  1 ;  number  needed  by  plants, 
95 ;  table  of  the  more  common,  3 

Chemical  formulas,  2 

Chemical  symbols,  2 

Chlorine,  characteristics  of,  9 ;  in 
plants,  100 

Chlorophyll,  75 

Chloroplasts,  75 

Chromoplasts,  78 

Cion,  effects  of  stock  on,  195 

Clay,  amount  of  pore  space  in,  41 ; 
characteristics  of,  31 ;  run-off  of 
water  in,  47 


291 


292 


AGRONOMY 


Cleavage  planes,  78 

Cold,  artificial  protection  from,  119  ; 
effect  of,  on  plants,  117 ;  protection 
from,  118 

Cold  frames,  120;  use  of,  161 

Contraction  wrinkles,  61 

Cool-season  plants,  134 

Corolla,  79 

Cotyledons,  86 

Crops,  grain,  282;  leaf,  279;  root, 
279 

Cross  pollination,  82 

Crossing,  262 

Cultivated  plants,  origin  of,  277 

Cuttings,  green  or  softwood,  185 ; 
growing  in  shade,  189  ;  hardwood, 
185;  heel,  188;  leaf,  186;  mallet, 
189  ;  method  of  making,  185 ;  prop- 
agation by,  185  ;  root,  187 ;  single 
eye,  188;  stem,  186;  tuber,  186; 
use  of,  184 

Darwinian  theory,  275 

Decorative  planting,  purpose  of,  197 

Delta  soils,  20 

Dew,  116 

Dew  point,  116 

Dibber,  141 

Dicotyledon  flower,  plan  of,  83 

Digestion  in  plants,  76 

Double  cropping,  138  ;  crops  for,  139 

Ducts,  in  stems,  66 ;  in  roots,  60 

Earth,  composition  of,  1 
Elementary  species,  91,  276 
Embryo,  86 
pjudosperm,  86 
Enzymes,  76 
Epidermal  hairs,  118 
Essential  organs,  80 
Evolution,  nature  of,  272 

Fahrenheit  scale,  43;  rule  for  chang- 
ing, to  centigrade,  44 

Fairy  rings,  102 

Families,  plant,  91 

Fertilization,  79  ;  double,  268 

Fertilizers,  effect  on  soil,  103  ;  how 
to  apply,  105 

Flower,  epigynous,  79  ;  hypogynous, 
79  ;  parts  of,  79 

Flowers,  characteristics  of  insect- 
pollinated,  82  ;  characteristics  of 
wind-pollinated,  82  ;  insect-polli- 
nated, 81 ;  wind-pollinated,  80 


Forcing  plants,  in  the  window  gar- 
den, 16^;  methods  of,  157,  162 
Forcing  single  hills,  161 
Formal  style  of  planting,  208 
Frost,  conditions  favoring,  116;  dif- 
ference from  dew,  116;   effect  of 
locality  on  formation  of,  116  ;  pro- 
tecting from,  116 
Frostbitten  plants,  treatment  of,  120 
Fruit,   a   result  of  pollination,   83; 
parts  of  the  flower  represented  in, 
83,  85 ;  seedless,  83 
Fruit  spurs,  220 
Fruiting,  how  induced,  141 
Fruits,  bush,  282  ;  gourd,  281 ;  modi- 
fied for  wind  distribution,  84,  85 ; 
new,  283  ;  purpose  of,  85  ;  s<jlana- 
ceous,  281 ;  tree,  282 

Garden  styles,  209 

Garden,  arrangement  of  crops  in, 
130 ;  location  of,  129 ;  plan  of, 
130,  135,  139 ;  planting,  132 ;  pre- 
paring the  soil  in,  130;  time  of 
planting,  134 ;  tools,  151,  154 

Genera,  90 

Geophilous  habit,  118 

Germination,  136 

Girdling,  227 

Glaciers,  work  of,  20 

Gourd  fruits,  281 

Graft  hybrids,  195 

Grafting,  bridge,  193;  cleft,  192; 
crown,  193 ;  f ormsof ,  192 ;  root,  194 ; 
saddle,  193  ;  splice,  193  ;  tongue, 
193;  value  of,  192;  veneer,  193; 
whip,  192 

Grafting  wax,  195 

Grain  crops,  282 

Gravel,  31 

Guard  cells,  74 

Guttation,  97 

Half-hardy  plants,  114 

Hardwood  cuttings,  187  ;  heel,  188  ; 

mallet,  188  ;  single  eye,  188 
Hardy  plants,  114  ;  sowing  seeds  of, 

136 
Heading  in,  224  ;  methods  of,  226 
Heat,  amount  received  from  sun,  41 ; 

effect  on  plants,  120 ;   protection 

from,  121 
Hedges,  plants  for,  207 
Heeling  in,  211 
Hilum,  86 


INDEX 


293 


Hotbeds,  159 

Humid  regions,  11 

Huimis,  30;    a  source  of  nitrogen, 

107  ;   effect  on  soil,  39,  43 
Hybridizing,  262 ;  how  accomplished, 

263 
Hybrids,  262  ;  method  of  producing, 

263 
Hydrogen,  characteristics  of,  8 
Hydrophytes,  126  ;  xerophytic,  127 

Inarching,  194 

Insects,  damage  to  plants  f  i-om,  245  ; 
forms  that  cause  injury,  246  ;  meta- 
morphoses of,  245 ;  methods  of 
combating,  255  ;  poisons  for,  252  ; 
preventing  attacks  of,  252  ;  smoth- 
ering sprays  for,  254 

Insects,  helpful  :  ant  lion,  256 ; 
dragon  fly,  256 ;  ichneumon  fly, 
256 ;  ladybird,  256 ;  ladybug,  256  ; 
spiders,  256  ;  tiger  beetle,  256 

Insects,  injurious:  blister  beetles,  250; 
borers,  249 ;  cabbage  worm,  247  ; 
cankerworm,  249;  codlin  moth, 
249  ;  corn-ear  worm,  248  ;  cucum- 
ber beetle,  250  ;  curculio,  249;  cur- 
rant worm,  248  ;  cixtworm,  247  ; 
elm-leaf  beetle,  250;  May  beetle, 
250 ;  mealy  bug,  251 ;  plant  lice, 
251  ;  potato  beetle,  250;  scale  in- 
sect, 251  ;  squash  bug,  251 ;  tent 
caterpillar,  248 ;  tomato  worm,  247 

Insects,  poisons  for :  arsenate  of  lead, 
253  ;  Paris  green,  252  ;  white  helle- 
bore, 252 

Insects,  smothers  for :  carbon  disul- 
phide,  254 ;  hydrocyanic  gas,  254  ; 
kerosene  emulsion,  254 ;  Persian 
insect  powder,  254 ;  tobacco  smoke, 
254 ;  tobacco  water,  254  ;  whale- 
oil  soap,  254 

Intercellular  spaces,  73 

Iron,  characteristics  of,  7 ;  in  plants, 
99 

Labels,  forms  of,   143;    method   of 

writing,  141 
Lath  houses,  123 
Lawn,  care  of,  201 ;   how  to  make, 

198;  paths  in,  199;  seeding,  198; 

sodding,  199 
Layering,  air,  189  ;  forms  of,  188  ; 

mound,  189  ;  nature  of,  188  ;  pot, 

189;  tip,  188;  vine,  188 


Leaf  crops,  279 

Leaves,  branching,  72  ;  epidermis  of, 

72  ;  fall  of,  77  ;  structure  of,  71, 

73  ;  veining  of,  72 

Legumes,  as  food,  280 ;  and  bacteria, 

108,  110 
Leucoplasts,  77 
Life  cycle  of  plants,  87 
Light,  effect  of  lack  of,  122  ;  needed 

by  plants,  122 ;  protection  from, 

123 
Lime,  effect  on  soil,  39 
Lime  plants,  7,  99 
Loam,  34 

Magnesium,  characteristics  of,  6  ;  in 

plants,  99 
Manganese,  characteristics  of,  7  ;  in 

plants,  100 
Mantle   rock,    12 ;    changes  in,  22 ; 

turned  to  soil,  23 
Manure,  derivation  of  the  word,  106 ; 

green,  106 
Marl,  30 

Medullary  rays,  67 
Mendel's  law,  264  ;  Illustrations  of, 

265 
Mesophytes,  127 
Metals,  and  nonmetals,  1 ;  properties 

of,  2 
Micropyle,  86 
Molecules,  2 

Monocotyledon  flower,  plan  of,  83 
Mulch,  dust  or  summer,  152 
Mulching,  120,  152,  211 
Mutation  theory,  275 
Mutations,  261 
Mycorrhizas,  109  ;  plants  associated 

with,  109 

Nectar  guides,  82 

Nitrates,  108 

Nitrification,  106;  bacteria  concerned 
in,  107 

Nitrites,  108 

Nitrogen,  characteristics  of,  8  ;  fixa- 
tion of,  108  ;  source  of,  105  ;  use 
of,  by  plants,  98 ;  value  of,  106 

Nonmetals,  examples  of,  2 

Nucleus,  58 

Orders,  91 

Osmosis,  63  ;  in  the  plant,  63 

Ovary,  79 

Overwatering,  effect  of,  124 


294 


AGRONOMY 


Ovules,  79 

Oxygen,  characteristics  of,  8 

Palisade  tissue,  73 

Parasites,  230  ;  wound,  238 

Parenchyma,  73 

Parthenogenesis,  269 

Peat,  29 

Pebbles,  31 

Perennials,  88 ;  arrangement  of,  206 ; 
herbaceous,  89  ;  use  of  herbaceous, 
206 ;  woody,  89 

Petals,  79 

Petiole,  71 

Phloem,  66 

Phosphorus,  characteristics  of,  9 ; 
source  of,  105  ;  use  of,  to  plant,  99 

Photosynthesis,  75  ;  contrasted  with 
respiration,  76 

Pith  cells,  65 

Plan  of  the  flower,  83 

Plant  breeding,  advantages  of,  258  ; 
basis  for,  259  ;  results  of,  267 

Plant   diseases,    blights,    234 ;    how 
caused,  230 ;  leaf  spots,  234  ;  meth- 
ods of  preventing,  243;  mildews 
235  ;  molds,  235  ;  number  of,  232 
rots,  233  ;  rusts,  237  ;  smuts,  237 
variety,  239  ;  wilts,  233 

Plant  food,  distribution  of,  76 ;  for- 
mation of,  75 ;  source  of  the  ele- 
ments in,  75,  97,  105 ;  storage  of, 
76 

Plant  growth,  limiting  factors  in.  111, 
114 

Plant  hairs,  118 

Plant  houses,  158 ;  how  heated,  159 

Plants,  antagonisms  of,  103 ;  cellvilar 
structure  of,  57  ;  edible  parts  of, 
278  ;  effects  of  cold  on,  117  ;  effects 
of  overwatering,  124  ;  life  cycle  of, 
87;  regions  of,  57;  relationships  of , 
90 ;  rest  period  of,  89 ;  time  to 
water,  124  ;  variations  in,  259 

Plowing,  150 

Pollarding,  225 

Pollen,  79  ;  of  wind-pollinated  flow- 
ers, 82 

Pollination,  79 ;  agencies  for,  80 ; 
organs  necessary  for,  80  ;  second- 
ary effects  of,  83 

Potash  plants,  99 

Potassium,  characteristics  of,  5 ; 
sources  of,  105 ;  use  of,  to  plants, 


Practical  exercises,  10,  24, 36,  53,  92, 
100,  112,  128,  147,  156,  163,  180, 
196,  214,  228r  243,  257,  269,  276, 
283 

Precipitation,  44 

Pricking  out,  141 

Propagation,  artificial,  183 ;  by  cut- 
tings, 184 ;  forms  designed  for, 
182  ;  natural  methods  of,  181 

Pi'opagation,  forms  for:  bulblet,  183 ; 
cormel,  183 ;  offset,  182  ;  rootstock, 
182  ;  runner,  182  ;  stolon,  182  ; 
sucker,  182  ;  tuber,  182 

Pruning,  implements  for,  217  ; 
methods  of,  217,  218;  plants  that 
do  not  need,  218;  purpose  of,  215  ; 
season  for,  216,  220  ;  special  crops, 
219 

Rainfall,  annual,  in  United  States,  46 ; 
distribution  of,  in  United  States, 
44,  45 ;  distribution  of,  in  world,  45 

Receptacle,  79 

Respiration  in  plants,  76 

Rest  period  of  plants,  89 

Retarding  plants,  157 

Ribbon  bedding,  208 

Rocks,  aqueous,  21  ;  igneous,  21  ; 
metamorphic,  21 ;  sedimentary,  21 ; 
table  of,  22 

Roguing,  268 

Root  crops,  279 

Root  grafting,  194 

Root  hairs,  absorption  by,  63  ;  ad- 
vantage of,  62  ;  structure  of,  62 

Root  pressure,  97 

Root  pruning,  226 

Root  system,  axial,  60;  inaxial,  60; 
of  corn,  58,  59 

Roots,  central  cylinder  in,  60 ;  cortex 
of,  60  ;  ducts  in,  60 ;  epidermis  of, 
60 ;  extent  of,  59 ;  multiple  primary, 
60  ;  structure  of,  59,  60 

Rose,  green,  64 

Rotation  of  crops,  character  of,  155  ; 
reason  for,  155 

Run-off,  47 

Sand,  amount  of  pore  space  in,  41  ; 

characteristics  of,  31,  33;  run-off 

of  water  on,  47 
Saprophytes,  230 
Scientific  names,  91 
Seed  packets,  how  to  close,  146  ;  how 

to  make,  146 


INDEX 


295 


Seed  tester,  138 

Seeds,  advantages  of,  85  ;  conditions 
needed  for  germination,  136 ;  deptli 
to  plant,  134  ;  drying,  144  ;  plant- 
ing table  for,  145  ;  receptacle  for, 
137  ;  saving,  144  ;  structure,  86  ; 
vitality  of,  137 

Selection,  artificial,  266 ;  natural, 
273 

Selective  absorption,  95 

Self-pollination,  82 

Self-pruning,  122 

Sepals,  79 

Shade  plants,  122  ;  artificially  pro- 
tected, 123 

Shearing  plants,  141 

Shrubs,  66  ;  for  winter  effects,  204  ; 
location  of,  on  lawns,  202 ;  naming, 
204 

Sieve  tubes,  66 

Silicon,  characteristics  of,  10 ;  in 
plants,  100 

Silt,  31 

Sodium,  characteristics  of,  6 ;  in 
plants,  100 

Soil,  absorption  of  water  by,  46 ; 
seolian,  28  ;  alluvial,  29 ;  amount 
of  chemical  elements  in,  38 ;  bac- 
teria in,  11,  107;  capillarity  in, 
47 ;  colluvial,  28.;  constituents, 
29;  definition  of,  11;  depth  of, 
11  ;  drift,  13  ;  effects  of  ants  on, 
154 ;  effects  of  earthworms  on, 
154  ;  effects  of  lime  on,  39  ;  effects 
of  puddling,  151 ;  flocculated,  38  ; 
glacial,  29  ;  harmful  organisms  in, 
110 ;  inorganic,  31 ;  lacustrine,  27  ; 
methodsof  pulverizing,  150;  names 
of,  25  ;  organic,  31  ;  origin  of,  12, 
25 ;  puddled,  39 ;  puddled,  and 
plants,  39 ;  residual,  12  ;  sedentary, 
26  ;  structure  of,  38  ;  temperature 
of,  42  ;  toxic  substances  in,  101  ; 
treatment  for  harmful  organisms 
in,  111  ;  ventilation  of,  41  ;  vol- 
canic, 28  ;  water  in,  47  ;  weather- 
ing of,  11 

Soil  crumbs,  38 

Soil  inoculation,  109 

Soil  maps,  34 

Solanaceous  fruits,  281 

Species,  90  ;  elementary,  91,  270 

Spermatophytes,  56 

Spores,  57  ;  number  of,  231 

Sports,  255 


Spray  pumps,  255 

Sprays  :  ammoniacal  copper  carbon- 
ate, 242  ;  Bordeaux  mixture,  240  ; 
copper  sulphate,  168 ;  iron  sul- 
phate, 168 ;  kerosene  emulsion, 
254 ;  lime-sulphur  wash,  241  ; 
potassium  sulphide,  243  ;  tobacco 
water,  254  ;  whale-oil  soap,  254 

Starch  grains,  75 

Stems,  forms  of,  64 ;  how  increased 
in  diameter,  67  ;  internodes,  71  ; 
nodes  of,  71  ;  structure  of,  65 ; 
use  of,  64 

Stigma,  79 

Stipules,  forms  of,  71 

Stock,  effects  on  cion,  195 

Stomata,  73,  74 ;  number  in  leaves, 
75  ;  use  of,  74 

Struggle  for  existence,  results  of, 
273 

Subsoil,  how  distinguished,  12 

Subsoil  ing,  150 

Sugar,  grape,  75  ;  turned  to  starch,  76 

Sulphur,  characteristics  of,  9 ;  in 
plants,  99 

Summer  annuals,  87 

Sun,  amount  of  heat  from,  41  ;  dis- 
tribution of  rays,  42 

Sunlight,  distribution  of,  41 

Survival  of  the  fittest,  273 

Symbiosis,  108 

Taproots,  65 

Temperature,    41  ;     adjustment    of 

plants  to,  113  ;  distribution  of,  41  ; 

effects  of  color  on,  43  ;  maximum, 

115;    minimum,   115;    of  growth 

processes,    114;     optimum,     115; 

variations  in,  42 
Tender  plants,  115 
Testa,  86 
Thermal  belt,  47 
Thinning,  142,  221 
Tillage,  effects  of,'  149 ;  purpose  of, 

149 
Topiary  work,  228 
Toxic  substances  in  soils,  101 
Transpiration,  how  plants  avoid,  77  ; 

use  of,  77 
Transplanting,  advantages  of,   140 ; 

implements   for,    140 ;    seedlings, 

139  ;  trees  and  shrubs,  209  ;  when 

performed,  140 
Trees,  89 
Trenching,  150 


296 


AGRONOMY 


Vacuoles,  67 

Variation,  how  induced,  261 ;  results 
of,  274 

Venation,  netted,  72  ;  palmate,  72  ; 
parallel,  72 ;  pinnate,  72 ;  reticu- 
lated, 72 

Verdant  zone,  117 

Vines,  methods  of  climbing,  89 

Warm-season  plants,  134 

Water,  amount  in  plant  parts,  97 ; 
amount  transpired  by  plants,  90  ; 
as  a  weathering  agent,  14,  18; 
capillary,  47  ;  hygroscopic,  47  ; 
percolating,  47  ;  plant  form  and, 
125  ;  use  of,  to  plants,  96 

Weathering,  by  decomposition,  13  ; 
by  disintegration,  16 

Weathering  agents,  13,  17 

Weeds,  distribution  of,  179 ;  harm- 
fulness  of,  165,  166  ;  how  to  eradi- 
cate, 167;  less  harmful,  178;  origin 
of,  164  ;  sprays  for,  108 


Weeds,  injurious:  black  bindweed, 
1 72 ;  buttercup,  1 76 ;  Canada  this- 
tle, 174;  common  bindweed,  172 
crab  grass,  175;   dandelion,  171 
foxtail,  176;  green  amaranth,  170 
old  witch  grass,  176;  oxeye  daisy 
174  ;  pigweed,  170  ;  plantain,  171 
prickly  lettuce,  173 ;  purslane,  169 
quack  gra&s,   175;  ragweed,  173 
sorrel,  177;  spotted  spurge,  170 
spreading  amaranth,  109;  tumV)le- 
weed,  170  ;  wild  carrot,  170  ;  wild 
mustard,  173 

Windbreaks,  120 

Winter  annuals,  87 

Woodlands,  enemies  of,  213  ;  value 
of,  212 

Xenia,  268 
Xerophytes,  125 
Xerophytic  hydrophytes,  127 

Zero,  upper,  middle,  and  lower,  115 


ANNOUNCEMENTS 


BOOKS   IN   BOTANY 


REPRESENTATIVE   PLANTS 

By  H.  S.  Pepoon,  Head  Instructor  in  Botany,  Lake  View  High 
School,  Chicago,  111. 

i2mo,  cloth,  163  pages,  60  cents 

A  MODERN  and  practical  study  of  the  seed  plants,  for  use  in  high- 
school  classes  beyond  the  first  year  and  in  the  elementary  courses  of 
the  smaller  colleges,  is  offered  in  this  new  manual  of  botany.  It  is 
based  upon  the  pupil's  knowledge  of  everyday  forms,  and  is  arranged 
under  the  divisional  heads  of  seeds,  roots,  stems,  leaves,  flowers,  and 
fruits.  Copious  applications  and  illustrations  of  each  new  botanical 
fact,  an  abundance  of  practical  work  for  the  laboratory,  and  many 
and  varied  examples  of  the  processes  by  which  the  products  of  common 
plants  are  prepared  for  use  constitute  features  of  distinct  progress. 

While  the  major  portion  of  the  book  is  devoted  to  seed  plants,  a 
presentation  of  the  evolution  of  spore  plants  and  of  the  principles  of 
ecology  completes  the  broad,  general  view  of  the  plant  kingdom 
which  may  be  obtained  from  a  use  of  this  text. 


LABORATORY   BOTANY 

By  WiLLARD  N.  Clute 
i2mo,  cloth,  xiv  +  177  pages,  75  cents 

For  the  teacher  who  is  crowded  for  time  or  the  student  who 
desires  to  do  independent  work,  Clute's  "  Laboratory  Botany  "  will 
be  found  invaluable.  The  manual  covers  a  year's  work.  It  is  made 
up  of  clear  and  accurate  outlines  of  the  specific  subjects,  such  as 
root,  stem,  flower,  fungi,  bryophytes,  gymnosperms,  etc. ;  directions 
for  examining  ;  and  lists  of  definite  questions  which  will  bring  out  all 
the  different  points  of  the  student's  investigation.  In  addition  it  con- 
tains a  key  for  outdoor  work  with  trees,  outlines  for  a  study  of  floral 
ecology,  and  tables  of  the  principal  families  and  larger  groups  of  the 
plant  world.  It  is  absolutely  flexible,  and  can  be  condensed  or  ex- 
tended by  individual  teachers  at  any  point  without  detriment  to 
the  work. 

149  a 

GINN  AND   COMPANY  Publishers 


NATURE  STUDY  AND  LIFE 

By  Clifton  F.  Hooge,  Professor  of  Biology  in  Clark  University,  Worcester,  Mass. 
With  an  Introduction  by  Dr.  G.  Stanley  Hall 

Cloth,  514  pages,  illustrated,  $1.50 

OUTLINE    FOR    HODGE'S    NATURE    STUDY    AND    LIFE 

Paper,  32  pages,  10  cents 

I\  the  point  of  view,  in  the  selection  of  the  subject  matter,  and 
in  the  presentation  of  methods  of  conducting  the  work,  "  Nature 
Study  and  Life  "  marks  a  definite  advance  over  earlier  publications 
on  the  subject  of  nature  study.  It  is  an  earnest  effort  to  give  funda- 
mental and  universal  interests  in  nature  their  deserved  place  in  our 
system  of  public  education.  It  presents  concrete  lessons  on  the  ani- 
mals and  plants  that  form  the  natural  environment  of  the  home. 
Each  form  is  studied  alive  and  at  work,  as  a  life  story  to  be  read  at 
first  hand  in  nature. 


GARDENS  AND  THEIR  MEANING 

By  Dora  Williams,  Boston  Normal  School 
8vo,  cloth,  ix  4-  235  pages,  $1.00 

This  little  manual  of  school  gardening  for  teachers  not  only  offers 
detailed  directions  for  the  scientific  management  of  gardens,  but  dis- 
cusses also  their  cultural  significance.  Loyalty,  cooperation,  and 
efficiency  are  some  of  the  lessons  stressed.  Miss  Williams's  point  of 
view  is  so  fresh  and  earnest  that  it  cannot  fail  to  be  illuminating 
and  inspiring. 

GINN  AND   COMPANY  Publishers 


AGRICULTURE    FOR 
BEGINNERS 

By  C.  W.  BuRKKTT,  recently  Director  of  Agricultural  Experiment  Station, 

Manhattan,  Kans;   F.  L.  Stevens,   Professor  of  Biology  in  the 

North  Carolina  College  of  Agrriculture  and  Mechanic  Arts  ; 

and  D.  H.  Hill,  President  of  the  North  Carolina 

College  of  Agriculture  and  Mechanic  Arts 


izmo,  cloth,  339  pages,  with  color  pictures,  illustrated,  75  cents 


NO  book  for  common  schools  in  recent  years  has  aroused 
such  widespread  interest  and  been  so  universally  com- 
mended as  this  little  volume.  Its  adoption  in  two  great 
states  before  its  publication,  and  in  still  another  state  immediately 
after  its  appearance,  indicates  the  unusually  high  merit  of  the  work. 

The  authors  believe  that  there  is  no  line  of  separation  between 
the  science  of  agriculture  and  the  practical  art  of  agriculture,  and 
that  the  subject  is  eminently  teachable.  Theory  and  practice  are 
presented  at  one  and  the  same  time,  so  that  the  pupil  is  taught  the 
fundamental  principles  of  farming  just  as  he  is  taught  the  funda- 
mental truths  of  arithmetic,  geography,  or  grammar. 

The  work  is  planned  for  use  in  grammar-school  classes.  It  thus 
presents  the  subject  to  the  pupil  when  his  aptitudes  are  the  most 
rapidly  developing  and  when  he  is  forming  life  habits.  It  will  give 
to  him,  therefore,  at  the  vital  period  of  his  life  a  training  which 
will  go  far  toward  making  his  life  work  profitable  and  delightful. 
The  text  is  clear,  interesting,  and  teachable.  While  primarily 
intended  for  class  work  in  the  public  schools,  it  will  no  doubt 
appeal  to  all  who  desire  a  knowledge  of  the  simple  scientific  truths 
which  lie  at  the  foundation  of  most  farm  operations. 

The  two  hundred  and  eighteen  illustrations  are  unusually  excel- 
lent and  are  particularly  effective  in  illuminating  the  text.  The 
book  is  supplied  throughout  with  practical  exercises,  simple  and 
interesting  experiments,  and  helpful  suggestions.  The  Appendix, 
devoted  to  spraying  mixtures  and  fertilizer  formulas,  the  Glossary, 
in  which  are  explained  unusual  and  technical  words,  and  the 
complete  Index  are  important. 

In  mechanical  execution  —  in  the  attractive  and  durable  bind- 
ing, in  the  clear,  well-printed  page,  and  in  the  illustrations  —  the 
^  book  is  easily  superior  to  any  other  elementary  work  on  agriculture. 

GINN    &    COMPANY    Publishers 


MEIER'S   NOTEBOOKS 

By  W.  H.  D.  Meier,  Assistant  in  Botany,  Harvard  University 


HERBARIUM  AND  PLANT  DESCRIPTION 

With  directions  for  collecting,  pressing,  and  tnounting  specimens.  A  loose-leaf 
cover  containing  25  sheets  for  description  and  preservation  of  specimens,  60  cents. 
In  Biflex  Binder,  65  cents. 

CCHOOLS  that  employ  the  herbarium  method  in  the  study  of  botany 
will  find  this  book  admirably  suited  to  their  needs. 

The  use  of  the  Biflex  Binder  as  a  cover  provides  an  attractive  and 
durable  loose-leaf  book,  and  the  twenty-five  sheets  for  the  mounting  of 
pressed  specimens  include  blank  forms  for  descriptions,  classifications, 
and  drawings.  Directions  for  collecting,  pressing,  and  mounting,  and  a 
list  of  terms  used  in  plant  description  are  given  on  a  separate  sheet. 

Those  who  desire  more  sheets  than  are  contained  in  the  cover  may 
obtain  them  in  packages  of  twenty-five,  accompanied  by  an  index  sheet. 
Price,  25  cents. 

PLANT    STUDY    (Revised  Edition) 

By  W.  H.  D.  Meier.  Biflex  Binder  containing  36  plant  studies,  with  space  for 
drawings,  18  sheets  ruled  on  both  sides  for  notes,  and  10  sheets  for  description 
and  preservation  of  specimens,  75  cents.   Plant  Study  Sheets  (pages  1-36),  25  cents. 

TVTEIER'S  "Plant  Study"  offers  ample  material  for  the  laboratory 
work  required  in  botany  for  entrance  to  the  leading  colleges  and 
universities.    It  is  perhaps  the  first  book  of  the  sort  to  serve  the  double 
purpose  of  both  notebook  and  herbarium. 

The  book  is  divided  into  pages  devoted  to  a  study  of  the  fundamental 
principles  of  plant  forms  and  their  classification,  with  space  left  for 
drawings.  Extra  ruled  sheets  are  provided  for  notes.  There  are  also 
pages  for  the  description,  classification,  and  preservation  of  specimens, 
with  accompanying  directions. 

ANIMAL  STUDY 

Biflex  Binder  containing  36  animal  studies,  with  space  for  drawings,  16  extra  draw- 
ing sheets,  and  36  note  sheets,  ruled  on  both  sides.    Price,  75  cents. 

TV/TEIER'S  "Animal  Study"  includes  the  principles  of  zoology  which 
are  indispensable  to  a  general  survey  of  the  science.  It  offers  an 
excellent  course  for  students  who  do  not  intend  to  continue  their  studies 
in  more  advanced  courses,  and  it  also  meets  the  requirements  in  zoology 
of  the  College-Entrance  Examination  Board. 


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